预先（AOT）编译器link

The Ahead-of-Time (AOT) compilerlink

Angular 应用主要由组件及其 HTML 模板组成。由于浏览器无法直接理解 Angular 所提供的组件和模板，因此 Angular 应用程序需要先进行编译才能在浏览器中运行。

An Angular application consists mainly of components and their HTML templates. Because the components and templates provided by Angular cannot be understood by the browser directly, Angular applications require a compilation process before they can run in a browser.

在浏览器下载和运行代码之前的编译阶段，Angular 预先（AOT）编译器会先把你的 Angular HTML 和 TypeScript 代码转换成高效的 JavaScript 代码。 在构建期间编译应用可以让浏览器中的渲染更快速。

The Angular Ahead-of-Time (AOT) compiler converts your Angular HTML and TypeScript code into efficient JavaScript code during the build phase before the browser downloads and runs that code. Compiling your application during the build process provides a faster rendering in the browser.

本指南中解释了如何指定元数据，并使用一些编译器选项以借助 AOT 编译器来更有效的编译应用。

This guide explains how to specify metadata and apply available compiler options to compile your applications efficiently using the AOT compiler.

Angular 中的编译link

Angular compilationlink

Angular 提供了两种方式来编译你的应用：

Angular offers two ways to compile your application:

1. 即时编译 (JIT)，它会在运行期间在浏览器中编译你的应用。

   Just-in-Time (JIT), which compiles your app in the browser at runtime.

2. 预先（AOT）编译，它会在构建时编译你的应用。

   Ahead-of-Time (AOT), which compiles your app at build time.

当你运行 ng build（仅编译）或 ng serve（编译并启动本地服务器） 这两个 CLI 命令时 JIT 编译是默认选项：

JIT compilation is the default when you run the ng build(build only) or ng serve(build and serve locally) CLI commands:

      
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      ng build
ng serve
    

要进行 AOT 编译，只要让 ng build 或 ng serve 命令中包含 --aot 标志就行了：

For AOT compilation, include the --aot option with the ng build or ng serve command:

      
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      ng build --aot
ng serve --aot
    

为什么需要 AOT 编译？link

Why compile with AOT?link

渲染得更快

Faster rendering

使用 AOT，浏览器下载预编译版本的应用程序。 浏览器直接加载运行代码，所以它可以立即渲染该应用，而不用等应用完成首次编译。

With AOT, the browser downloads a pre-compiled version of the application. The browser loads executable code so it can render the application immediately, without waiting to compile the app first.

需要的异步请求更少

Fewer asynchronous requests

编译器把外部 HTML 模板和 CSS 样式表内联到了该应用的 JavaScript 中。 消除了用来下载那些源文件的 Ajax 请求。

The compiler inlines external HTML templates and CSS style sheets within the application JavaScript, eliminating separate ajax requests for those source files.

需要下载的 Angular 框架体积更小

Smaller Angular framework download size

如果应用已经编译过了，自然不需要再下载 Angular 编译器了。 该编译器差不多占了 Angular 自身体积的一半儿，所以，省略它可以显著减小应用的体积。

There's no need to download the Angular compiler if the app is already compiled. The compiler is roughly half of Angular itself, so omitting it dramatically reduces the application payload.

提早检测模板错误

Detect template errors earlier

AOT 编译器在构建过程中检测和报告模板绑定错误，避免用户遇到这些错误。

The AOT compiler detects and reports template binding errors during the build step before users can see them.

更安全

Better security

AOT 方式会在发给客户端之前就把 HTML 模板和组件编译成 JavaScript 文件。 不需要读取模板，也没有客户端组装 HTML 或执行 JavaScript 的危险操作，受到注入类攻击的机会也比较少。

AOT compiles HTML templates and components into JavaScript files long before they are served to the client. With no templates to read and no risky client-side HTML or JavaScript evaluation, there are fewer opportunities for injection attacks.

控制应用的编译方式link

Controlling app compilationlink

当使用 Angular 的 AOT 编译器时，你可以通过两种方式来控制应用的编译方式：

When you use the Angular AOT compiler, you can control your app compilation in two ways:

• 在 tsconfig.json 文件中提供模板编译选项。

  By providing template compiler options in the tsconfig.json file.

  欲知详情，参见 Angular 模板编译器选项。

  For more information, see Angular template compiler options.

• 通过指定 Angular 元数据。

  By specifying Angular metadata.

指定 Angular 元数据link

Specifying Angular metadatalink

Angular 的元数据会告诉 Angular 如何创建应用中类的实例以及如何在运行期间与它们交互。 Angular 的 AOT 编译器会把元数据提取出来，以告诉 Angular 应该管理应用程序的哪些部分。

Angular metadata tells Angular how to construct instances of your application classes and interact with them at runtime. The Angular AOT compiler extracts metadata to interpret the parts of the application that Angular is supposed to manage.

你通过装饰器来指定元数据，比如 @Component() 和 @Input()。 你还可以在这些带装饰器的类的构造函数中隐式指定元数据。

You can specify the metadata with decorators such as @Component() and @Input() or implicitly in the constructor declarations of these decorated classes.

在下列范例中，@Component() 元数据对象和类的构造函数会告诉 Angular 如何创建和显示 TypicalComponent 的实例。

In the following example, the @Component() metadata object and the class constructor tell Angular how to create and display an instance of TypicalComponent.

      
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      @Component({
  selector: 'app-typical',
  template: '<div>A typical component for {{data.name}}</div>'
)}
export class TypicalComponent {
  @Input() data: TypicalData;
  constructor(private someService: SomeService) { ... }
}
    

Angular 编译器只提取一次元数据，并且为 TypicalComponent 生成一个工厂。 当它需要创建 TypicalComponent 的实例时，Angular 调用这个工厂，工厂会生成一个新的可视元素，并且把它（及其依赖）绑定到组件类的一个新实例上。

The Angular compiler extracts the metadata once and generates a factory for TypicalComponent. When it needs to create a TypicalComponent instance, Angular calls the factory, which produces a new visual element, bound to a new instance of the component class with its injected dependency.

元数据的限制link

Metadata restrictionslink

你只能使用 TypeScript 的一个子集书写元数据，它必须满足下列限制：

You write metadata in a subset of TypeScript that must conform to the following general constraints:

1. 表达式语法只支持 JavaScript 的一个有限的子集。

   Limit expression syntax to the supported subset of JavaScript.

2. 只能引用代码收缩后导出的符号。

   Only reference exported symbols after code folding.

3. 只能调用编译器支持的那些函数。

   Only call functions supported by the compiler.

4. 被装饰和用于数据绑定的类成员必须是公共（public）的。

   Decorated and data-bound class members must be public.

下一节将会详细解释这些问题。

The next sections elaborate on these points.

AOT 工作原理link

How AOT workslink

可以把 AOT 编译器看做两个阶段：在代码分析阶段，它只记录源代码，而在代码生成阶段，编译器的 StaticReflector 会解释这些结果，并为这些结果加上限制。

It helps to think of the AOT compiler as having two phases: a code analysis phase in which it simply records a representation of the source; and a code generation phase in which the compiler's StaticReflector handles the interpretation as well as places restrictions on what it interprets.

阶段 1：分析link

Phase 1: analysislink

TypeScript 编译器会做一些初步的分析工作，它会生成类型定义文件.d.ts，其中带有类型信息，Angular 编译器需要借助它们来生成代码。

The TypeScript compiler does some of the analytic work of the first phase. It emits the .d.ts type definition files with type information that the AOT compiler needs to generate application code.

同时，AOT 收集器（collector） 会记录 Angular 装饰器中的元数据，并把它们输出到.metadata.json文件中，和每个 .d.ts 文件相对应。

At the same time, the AOT collector analyzes the metadata recorded in the Angular decorators and outputs metadata information in .metadata.jsonfiles, one per .d.ts file.

你可以把 .metadata.json 文件看做一个包括全部装饰器的元数据的全景图，就像抽象语法树 (AST) 一样。

You can think of .metadata.json as a diagram of the overall structure of a decorator's metadata, represented as an abstract syntax tree (AST).

表达式语法link

Expression syntaxlink

收集器只能理解 JavaScript 的一个子集。 定义元数据对象时要遵循下列语法限制：

The collector only understands a subset of JavaScript. Define metadata objects with the following limited syntax:

如果表达式使用了不支持的语法，收集器就会往 .metadata.json 文件中写入一个错误节点。稍后，如果编译器用到元数据中的这部分内容来生成应用代码，它就会报告这个错误。

If an expression uses unsupported syntax, the collector writes an error node to the .metadata.json file. The compiler later reports the error if it needs that piece of metadata to generate the application code.

      
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      "angularCompilerOptions": {
  ...
  "strictMetadataEmit" : true
}
    

不要有箭头函数link

No arrow functionslink

AOT 编译器不支持 函数表达式 和 箭头函数（也叫 Lambda 函数）。

The AOT compiler does not support function expressions and arrow functions, also called lambda functions.

考虑如下组件装饰器：

Consider the following component decorator:

      
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      @Component({
  ...
  providers: [{provide: server, useFactory: () => new Server()}]
})
    

AOT 的收集器不支持在元数据表达式中出现箭头函数 () => new Server()。 它会在该函数中就地生成一个错误节点。

The AOT collector does not support the arrow function, () => new Server(), in a metadata expression. It generates an error node in place of the function.

稍后，当编译器解释该节点时，它就会报告一个错误，让你把这个箭头函数转换成一个导出的函数。

When the compiler later interprets this node, it reports an error that invites you to turn the arrow function into an exported function.

你可以把它改写成这样来修复这个错误：

You can fix the error by converting to this:

      
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      export function serverFactory() {
  return new Server();
}

@Component({
  ...
  providers: [{provide: server, useFactory: serverFactory}]
})
    

从 Angular v5 开始，编译器会在生成 .js 文件时自动执行这种改写。

Beginning in version 5, the compiler automatically performs this rewriting while emitting the .js file.

受限函数调用link

Limited function callslink

只要语法有效，收集器就可以支持函数调用或使用 new 来创建对象。收集器只在乎语法是否正确。

The collector can represent a function call or object creation with new as long as the syntax is valid. The collector only cares about proper syntax.

但要注意。编译器稍后可能拒绝调用特定的函数或拒绝创建特定的对象。 编译器值仅支持调用一小部分函数，也只能 new 一小部分类。这些函数和类列在了后面的表格中。

But beware. The compiler may later refuse to generate a call to a particular function or creation of a particular object. The compiler only supports calls to a small set of functions and will use new for only a few designated classes. These functions and classes are in a table of below.

折叠（fold）link

Foldinglink

编译器只能解析对导出的符号的引用。 幸运的是，收集器支持通过折叠来有限的使用那些未导出的符号。

The compiler can only resolve references to exported symbols. Fortunately, the collector enables limited use of non-exported symbols through folding.

收集器可以在收集期间执行表达式，并用其结果代替原始表达式，记录到 .metadata.json 中。

The collector may be able to evaluate an expression during collection and record the result in the .metadata.json instead of the original expression.

比如，收集器可以执行表达式 1 + 2 + 3 + 4，并使用它的结果 10 替换它。

For example, the collector can evaluate the expression 1 + 2 + 3 + 4 and replace it with the result, 10.

这个过程被称为折叠。能用这种方式进行简化的表达式就是可折叠的。

This process is called folding. An expression that can be reduced in this manner is foldable.

收集器可以计算对模块局部变量的 const 声明和初始化过的 var 和 let 声明，并从 .metadata.json 文件中移除它们。

The collector can evaluate references to module-local const declarations and initialized var and let declarations, effectively removing them from the .metadata.json file.

考虑下列组件定义：

Consider the following component definition:

      
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      const template = '<div>{{hero.name}}</div>';

@Component({
  selector: 'app-hero',
  template: template
})
export class HeroComponent {
  @Input() hero: Hero;
}
    

编译器不能引用 template 常量，因为它是未导出的。

The compiler could not refer to the template constant because it isn't exported.

但是折叠器可以通过内联 template 常量的方式把它折叠进元数据定义中。 最终的结果和你以前的写法是一样的：

But the collector can fold the template constant into the metadata definition by inlining its contents. The effect is the same as if you had written:

      
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      @Component({
  selector: 'app-hero',
  template: '<div>{{hero.name}}</div>'
})
export class HeroComponent {
  @Input() hero: Hero;
}
    

这里没有对 template 的引用，因此，当编译器稍后对位于 .metadata.json 中的收集器输出进行解释时，不会再出问题。

There is no longer a reference to template and, therefore, nothing to trouble the compiler when it later interprets the collector's output in .metadata.json.

你还可以通过把 template 常量包含在其它表达式中来让这个例子深入一点：

You can take this example a step further by including the template constant in another expression:

      
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      const template = '<div>{{hero.name}}</div>';

@Component({
  selector: 'app-hero',
  template: template + '<div>{{hero.title}}</div>'
})
export class HeroComponent {
  @Input() hero: Hero;
}
    

收集器把该表达式缩减成其等价的已折叠字符串：

The collector reduces this expression to its equivalent folded string:

'<div>{{hero.name}}</div><div>{{hero.title}}</div>'.

可折叠的语法link

Foldable syntaxlink

下表中描述了收集器可以折叠以及不能折叠哪些表达式：

The following table describes which expressions the collector can and cannot fold:

如果表达式是不可折叠的，那么收集器就会把它作为一个 AST（抽象语法树） 写入 .metadata.json 中，留给编译器去解析。

If an expression is not foldable, the collector writes it to .metadata.json as an AST for the compiler to resolve.

阶段 2：代码生成link

Phase 2: code generationlink

收集器不会试图理解它收集并输出到 .metadata.json 中的元数据，它所能做的只是尽可能准确的表述这些元数据，并在检测到元数据中的语法违规时记录这些错误。

The collector makes no attempt to understand the metadata that it collects and outputs to .metadata.json. It represents the metadata as best it can and records errors when it detects a metadata syntax violation.

解释这些 .metadata.json 是编译器在代码生成阶段要承担的工作。

It's the compiler's job to interpret the .metadata.json in the code generation phase.

编译器理解收集器支持的所有语法形式，但是它也可能拒绝那些虽然语法正确但语义违反了编译器规则的元数据。

The compiler understands all syntax forms that the collector supports, but it may reject syntactically correct metadata if the semantics violate compiler rules.

编译器只能引用已导出的符号。

The compiler can only reference exported symbols.

带有装饰器的类成员必须是公开的。你不可能制作一个私有或内部使用的 @Input() 属性。

Decorated component class members must be public. You cannot make an @Input() property private or internal.

数据绑定的属性同样必须是公开的。

Data bound properties must also be public.

      
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      // BAD CODE - title is private
@Component({
  selector: 'app-root',
  template: '<h1>{{title}}</h1>'
})
export class AppComponent {
  private title = 'My App'; // Bad
}
    

最重要的是，编译器生成代码时，只支持为下面列出的某些类创建实例、只支持某些装饰器、只会调用某些函数。

Most importantly, the compiler only generates code to create instances of certain classes, support certain decorators, and call certain functions from the following lists.

新建实例link

New instanceslink

编译器只允许创建来自 @angular/core 的 InjectionToken 类创建实例。

The compiler only allows metadata that create instances of the class InjectionToken from @angular/core.

注解 / 装饰器link

Annotations/Decoratorslink

编译器只支持下列 Angular 装饰器中的元数据。

The compiler only supports metadata for these Angular decorators.

宏函数或静态宏函数link

Macro-functions and macro-static methodslink

编译器也支持在返回表达式的函数或静态函数中使用宏。

The compiler also supports macros in the form of functions or static methods that return an expression.

考虑下面的函数：

For example, consider the following function:

      
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      export function wrapInArray<T>(value: T): T[] {
  return [value];
}
    

你可以在元数据定义中调用 wrapInArray，因为它所返回的表达式的值满足编译器支持的 JavaScript 受限子集。

You can call the wrapInArray in a metadata definition because it returns the value of an expression that conforms to the compiler's restrictive JavaScript subset.

你还可以这样使用 wrapInArray()：

You might use wrapInArray() like this:

      
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      @NgModule({
  declarations: wrapInArray(TypicalComponent)
})
export class TypicalModule {}
    

编译器会把这种用法处理成你以前的写法：

The compiler treats this usage as if you had written:

      
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      @NgModule({
  declarations: [TypicalComponent]
})
export class TypicalModule {}
    

收集器决定哪些函数是宏函数是很简单的 —— 它只能包含一个 return 语句。

The collector is simplistic in its determination of what qualifies as a macro function; it can only contain a single return statement.

Angular 的 RouterModule导出了两个静态宏函数 forRoot 和 forChild，以帮助声明根路由和子路由。 查看这些方法的源码，以了解宏函数是如何简化复杂的 NgModule 配置的。

The Angular RouterModuleexports two macro static methods, forRoot and forChild, to help declare root and child routes. Review the source code for these methods to see how macros can simplify configuration of complex NgModules.

元数据重写link

Metadata rewritinglink

编译器会对含有 useClass、useValue、useFactory 和 data 的对象字面量进行特殊处理。 编译器会把用这些字段之一初始化的表达式转换成一个导出的变量，并用它替换该表达式。 这个重写表达式的过程，会消除它们受到的所有限制，因为编译器并不需要知道该表达式的值，它只要能生成对该值的引用就行了。

The compiler treats object literals containing the fields useClass, useValue, useFactory, and data specially. The compiler converts the expression initializing one of these fields into an exported variable, which replaces the expression. This process of rewriting these expressions removes all the restrictions on what can be in them because the compiler doesn't need to know the expression's value—it just needs to be able to generate a reference to the value.

你可以这样写：

You might write something like:

      
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      class TypicalServer {

}

@NgModule({
  providers: [{provide: SERVER, useFactory: () => TypicalServer}]
})
export class TypicalModule {}
    

如果不重写，这就是无效的，因为这里不支持 Lambda 表达式，而且 TypicalServer 也没有被导出。

Without rewriting, this would be invalid because lambdas are not supported and TypicalServer is not exported.

为了允许这种写法，编译器自动把它重写成了这样：

To allow this, the compiler automatically rewrites this to something like:

      
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      class TypicalServer {

}

export const ɵ0 = () => new TypicalServer();

@NgModule({
  providers: [{provide: SERVER, useFactory: ɵ0}]
})
export class TypicalModule {}
    

这就让编译器能在工厂中生成一个对 ɵ0 的引用，而不用知道 ɵ0 中包含的值到底是什么。

This allows the compiler to generate a reference to ɵ0 in the factory without having to know what the value of ɵ0 contains.

编译器会在生成 .js 文件期间进行这种重写。它不会重写 .d.ts 文件，所以 TypeScript 也不会把这个变量当做一项导出，因此也就不会污染 ES 模块中导出的 API。

The compiler does the rewriting during the emit of the .js file. This doesn't rewrite the .d.ts file, however, so TypeScript doesn't recognize it as being an export. Thus, it does not pollute the ES module's exported API.

元数据错误link

Metadata errorslink

你可能遇到一些元数据错误，下面是对它们的解释和纠正建议。

The following are metadata errors you may encounter, with explanations and suggested corrections.

不支持此表达式格式Expression form not supported
引用了局部（未导出的）符号Reference to a local (non-exported) symbol
只允许初始化过的变量和常量Only initialized variables and constants
引用了未导出的类Reference to a non-exported class
引用了未导出的函数Reference to a non-exported function
不支持函数调用Function calls are not supported
不支持解构变量或常量Destructured variable or constant not supported
不能解析此类型Could not resolve type
期待是名字Name expected
不支持的枚举成员名Unsupported enum member name
不支持带标签函数的模板表达式Tagged template expressions are not supported
期待是符号引用Symbol reference expected

不支持这种表达式格式link

Expression form not supportedlink

编译器在对 Angular 元数据求值时遇到了一个它不能理解的表达式。

The compiler encountered an expression it didn't understand while evaluating Angular metadata.

除编译器允许的表达式语法之外的语言特性可能导致这个错误，比如下面的例子：

Language features outside of the compiler's restricted expression syntax can produce this error, as seen in the following example:

      
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      // ERROR
export class Fooish { ... }
...
const prop = typeof Fooish; // typeof is not valid in metadata
  ...
  // bracket notation is not valid in metadata
  { provide: 'token', useValue: { [prop]: 'value' } };
  ...
    

你可以在普通的应用代码中使用 typeof 和方括号标记法来指定属性名，但是这些特性不能在定义 Angular 元数据的表达式中使用。

You can use typeof and bracket notation in normal application code. You just can't use those features within expressions that define Angular metadata.

在写 Angular 的元数据时，严格遵循编译器的受限表达式语法可以避免这个错误，此外还要小心那些新的或罕见的 TypeScript 特性。

Avoid this error by sticking to the compiler's restricted expression syntax when writing Angular metadata and be wary of new or unusual TypeScript features.

引用了局部（未导出的）符号link

Reference to a local (non-exported) symbollink

编译器遇到了局部定义的未导出或未初始化的符号。

The compiler encountered a referenced to a locally defined symbol that either wasn't exported or wasn't initialized.

下面就是存在该问题的 provider 范例。

Here's a provider example of the problem.

      
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      // ERROR
let foo: number; // neither exported nor initialized

@Component({
  selector: 'my-component',
  template: ... ,
  providers: [
    { provide: Foo, useValue: foo }
  ]
})
export class MyComponent {}
    

编译器会在单独的模块中生成这个 userValue 提供商的代码。那个工厂模块不能访问这个源码模块，无法访问这个（未导出的）foo 变量。

The compiler generates the component factory, which includes the useValue provider code, in a separate module. That factory module can't reach back to this source module to access the local (non-exported) foo variable.

你可以通过初始化 foo 来修正这个错误。

You could fix the problem by initializing foo.

      
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      let foo = 42; // initialized
    

编译器将会把这个表达式折叠进 providers 中，就像你以前的写法一样。

The compiler will fold the expression into the provider as if you had written this.

      
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      providers: [
  { provide: Foo, useValue: 42 }
]
    

另外，你也可以通过导出 foo 来解决它，这样 foo 将会在运行期间你真正知道它的值的时候被赋值。

Alternatively, you can fix it by exporting foo with the expectation that foo will be assigned at runtime when you actually know its value.

      
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      // CORRECTED
export let foo: number; // exported

@Component({
  selector: 'my-component',
  template: ... ,
  providers: [
    { provide: Foo, useValue: foo }
  ]
})
export class MyComponent {}
    

添加 export 的方式通常用于需要在元数据中引用变量时，如 providers 和 animations，这样编译器就可以在这些表达式中生成对已导出变量的引用了。它不需要知道这些变量的值。

Adding export often works for variables referenced in metadata such as providers and animations because the compiler can generate references to the exported variables in these expressions. It doesn't need the values of those variables.

当编译器需要知道真正的值以生成代码时，添加 export 的方式就是无效的。比如这里的 template 属性。

Adding export doesn't work when the compiler needs the actual value in order to generate code. For example, it doesn't work for the template property.

      
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      // ERROR
export let someTemplate: string; // exported but not initialized

@Component({
  selector: 'my-component',
  template: someTemplate
})
export class MyComponent {}
    

编译器现在就需要 template 属性的值来生成组件工厂。 仅仅有对该变量的引用是不够的。 给这个声明加上 export 前缀只会生成一个新的错误 "Only initialized variables and constants can be referenced【只能引用初始化过的变量和常量】"。

The compiler needs the value of the template property right now to generate the component factory. The variable reference alone is insufficient. Prefixing the declaration with export merely produces a new error, "Only initialized variables and constants can be referenced".

只允许使用初始化过的变量和常量link

Only initialized variables and constantslink

编译器发现某个到已导出的变量或静态字段的引用是没有初始化过的。而它需要根据那个变量的值来生成代码。

The compiler found a reference to an exported variable or static field that wasn't initialized. It needs the value of that variable to generate code.

下面的例子试图把组件的 template 属性设置为已导出的 someTemplate 变量的值，而这个值虽然声明过，却没有初始化过。

The following example tries to set the component's template property to the value of the exported someTemplate variable which is declared but unassigned.

      
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      // ERROR
export let someTemplate: string;

@Component({
  selector: 'my-component',
  template: someTemplate
})
export class MyComponent {}
    

如果你从其它模块中导入了 someTemplate，但那个模块中忘了初始化它，就会看到这个错误。

You'd also get this error if you imported someTemplate from some other module and neglected to initialize it there.

      
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      // ERROR - not initialized there either
import { someTemplate } from './config';

@Component({
  selector: 'my-component',
  template: someTemplate
})
export class MyComponent {}
    

编译器不能等到运行时才得到该模板的信息。 它必须从源码中静态获得这个 someTemplate 变量的值，以便生成组件工厂，组件工厂中需要包含根据这个模板来生成元素的代码。

The compiler cannot wait until runtime to get the template information. It must statically derive the value of the someTemplate variable from the source code so that it can generate the component factory, which includes instructions for building the element based on the template.

要纠正这个错误，请在同一行的初始化子句中初始化这个变量的值。

To correct this error, provide the initial value of the variable in an initializer clause on the same line.

      
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      // CORRECTED
export let someTemplate = '<h1>Greetings from Angular</h1>';

@Component({
  selector: 'my-component',
  template: someTemplate
})
export class MyComponent {}
    

引用了未导出的类link

Reference to a non-exported classlink

元数据引用了一个未导出的类。

Metadata referenced a class that wasn't exported.

比如，你可能定义了一个类并在某个 providers 数组中把它用作了依赖注入令牌，但是忘了导出这个类。

For example, you may have defined a class and used it as an injection token in a providers array but neglected to export that class.

      
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      // ERROR
abstract class MyStrategy { }

  ...
  providers: [
    { provide: MyStrategy, useValue: ... }
  ]
  ...
    

Angular 会在一个单独的模块中生成类工厂，而那个工厂只能访问已导出的类。 要纠正这个问题，就要导出所引用的类。

Angular generates a class factory in a separate module and that factory can only access exported classes. To correct this error, export the referenced class.

      
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      // CORRECTED
export abstract class MyStrategy { }

  ...
  providers: [
    { provide: MyStrategy, useValue: ... }
  ]
  ...
    

引用了未导出的函数link

Reference to a non-exported functionlink

元数据中引用了未导出的函数。

Metadata referenced a function that wasn't exported.

比如，你可能已经把某个服务提供商的 useFactory 属性设置成了一个局部定义但忘了导出的函数。

For example, you may have set a providers useFactory property to a locally defined function that you neglected to export.

      
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      // ERROR
function myStrategy() { ... }

  ...
  providers: [
    { provide: MyStrategy, useFactory: myStrategy }
  ]
  ...
    

Angular 会在一个单独的模块中生成类工厂，那个工厂只能访问已导出的函数。 要纠正这个错误，请导出该函数。

Angular generates a class factory in a separate module and that factory can only access exported functions. To correct this error, export the function.

      
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      // CORRECTED
export function myStrategy() { ... }

  ...
  providers: [
    { provide: MyStrategy, useFactory: myStrategy }
  ]
  ...
    

不支持函数调用link

Function calls are not supportedlink

编译器目前不支持函数表达式或 Lambda 表达式。 比如，你不能把某个服务提供商的 useFactory 设置成如下匿名函数或函数表达式。

The compiler does not currently support function expressions or lambda functions. For example, you cannot set a provider's useFactory to an anonymous function or arrow function like this.

      
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      // ERROR
  ...
  providers: [
    { provide: MyStrategy, useFactory: function() { ... } },
    { provide: OtherStrategy, useFactory: () => { ... } }
  ]
  ...
    

如果你在某个提供商的 useValue 中调用函数或方法，也会导致这个错误。

You also get this error if you call a function or method in a provider's useValue.

      
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      // ERROR
import { calculateValue } from './utilities';

  ...
  providers: [
    { provide: SomeValue, useValue: calculateValue() }
  ]
  ...
    

要改正这个问题，就要从模块中导出这个函数，并改成在服务提供商的 useFactory 中引用该函数。

To correct this error, export a function from the module and refer to the function in a useFactory provider instead.

      
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      // CORRECTED
import { calculateValue } from './utilities';

export function myStrategy() { ... }
export function otherStrategy() { ... }
export function someValueFactory() {
  return calculateValue();
}
  ...
  providers: [
    { provide: MyStrategy, useFactory: myStrategy },
    { provide: OtherStrategy, useFactory: otherStrategy },
    { provide: SomeValue, useFactory: someValueFactory }
  ]
  ...
    

不支持解构变量或常量link

Destructured variable or constant not supportedlink

编译器不支持引用通过解构赋值的方式得到的变量。

The compiler does not support references to variables assigned by destructuring.

比如，你不能这么写：

For example, you cannot write something like this:

      
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      // ERROR
import { configuration } from './configuration';

// destructured assignment to foo and bar
const {foo, bar} = configuration;
  ...
  providers: [
    {provide: Foo, useValue: foo},
    {provide: Bar, useValue: bar},
  ]
  ...
    

要纠正这个错误，就要引用非解构方式的变量。

To correct this error, refer to non-destructured values.

      
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      // CORRECTED
import { configuration } from './configuration';
  ...
  providers: [
    {provide: Foo, useValue: configuration.foo},
    {provide: Bar, useValue: configuration.bar},
  ]
  ...
    

不能解析类型link

Could not resolve typelink

编译器遇到了某个类型，但是不知道它是由哪个模块导出的。

The compiler encountered a type and can't determine which module exports that type.

这通常会发生在你引用环境类型时。 比如，Window 类型就是在全局 .d.ts 文件中声明的环境类型。

This can happen if you refer to an ambient type. For example, the Window type is an ambient type declared in the global .d.ts file.

如果你在组件的构造函数中引用它就会导致一个错误，因为编译器必须对构造函数进行静态分析。

You'll get an error if you reference it in the component constructor, which the compiler must statically analyze.

      
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      // ERROR
@Component({ })
export class MyComponent {
  constructor (private win: Window) { ... }
}
    

TypeScript 能理解这些环境类型，所以你不用导入它们。 但 Angular 编译器不理解你没有导入或导出过的类型。

TypeScript understands ambient types so you don't import them. The Angular compiler does not understand a type that you neglect to export or import.

这种情况下，编译器就无法理解如何使用这个 Window 令牌来进行注入。

In this case, the compiler doesn't understand how to inject something with the Window token.

不要在元数据表达式中引用环境类型。

Do not refer to ambient types in metadata expressions.

如果你必须注入某个环境类型的实例，可以用以下四步来巧妙解决这个问题：

If you must inject an instance of an ambient type, you can finesse the problem in four steps:

1. 为环境类型的实例创建一个注入令牌。

   Create an injection token for an instance of the ambient type.

2. 创建一个返回该实例的工厂函数。

   Create a factory function that returns that instance.

3. 使用该工厂函数添加一个 useFactory 提供商。

   Add a useFactory provider with that factory function.

4. 使用 @Inject 来注入这个实例。

   Use @Inject to inject the instance.

下面的例子说明了这一点。

Here's an illustrative example.

      
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      // CORRECTED
import { Inject } from '@angular/core';

export const WINDOW = new InjectionToken('Window');
export function _window() { return window; }

@Component({
  ...
  providers: [
    { provide: WINDOW, useFactory: _window }
  ]
})
export class MyComponent {
  constructor (@Inject(WINDOW) private win: Window) { ... }
}
    

对于编译器来说，构造函数中出现 Window 类型已不再是个问题，因为它现在使用 @Inject(WINDOW) 来生成注入代码。

The Window type in the constructor is no longer a problem for the compiler because it uses the @Inject(WINDOW) to generate the injection code.

Angular 也用 DOCUMENT 令牌做了类似的事情，所以你也可以注入浏览器的 document 对象（或它的一个抽象层，取决于该应用运行在哪个平台）。

Angular does something similar with the DOCUMENT token so you can inject the browser's document object (or an abstraction of it, depending upon the platform in which the application runs).

      
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      import { Inject }   from '@angular/core';
import { DOCUMENT } from '@angular/platform-browser';

@Component({ ... })
export class MyComponent {
  constructor (@Inject(DOCUMENT) private doc: Document) { ... }
}
    

期待是名字link

Name expectedlink

编译器期待它正在求值的表达式中是一个名字。 如果你像下面的例子中这样用一个数字作为属性名，就会导致这个问题。

The compiler expected a name in an expression it was evaluating. This can happen if you use a number as a property name as in the following example.

      
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      // ERROR
provider: [{ provide: Foo, useValue: { 0: 'test' } }]
    

把该属性的名字改为非数字类型。

Change the name of the property to something non-numeric.

      
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      // CORRECTED
provider: [{ provide: Foo, useValue: { '0': 'test' } }]
    

不支持的枚举成员名link

Unsupported enum member namelink

Angular 不能确定你在元数据中引用的枚举成员的值。

Angular couldn't determine the value of the enum member that you referenced in metadata.

编译器可以理解简单的枚举值，但不能理解复杂的，比如从那些计算属性中派生出来的。

The compiler can understand simple enum values but not complex values such as those derived from computed properties.

      
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      // ERROR
enum Colors {
  Red = 1,
  White,
  Blue = "Blue".length // computed
}

  ...
  providers: [
    { provide: BaseColor,   useValue: Colors.White } // ok
    { provide: DangerColor, useValue: Colors.Red }   // ok
    { provide: StrongColor, useValue: Colors.Blue }  // bad
  ]
  ...
    

避免引用那些使用了复杂初始化对象或计算属性的枚举。

Avoid referring to enums with complicated initializers or computed properties.

不支持带标签函数的模板表达式link

Tagged template expressions are not supportedlink

当编译器遇到这样的带标签函数的模板表达式 时：

The compiler encountered a JavaScript ES2015 tagged template expression such as,

      
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      // ERROR
const expression = 'funky';
const raw = String.raw`A tagged template ${expression} string`;
 ...
 template: '<div>' + raw + '</div>'
 ...
    

String.raw()是一个 ES2015 原生的标签函数。

String.raw()is a tag function native to JavaScript ES2015.

AOT 编译器不支持带标签函数的模板表达式，避免在元数据表达式中使用它们。

The AOT compiler does not support tagged template expressions; avoid them in metadata expressions.

期待是符号引用link

Symbol reference expectedlink

编译器期待在错误信息指出的位置是一个符号引用。

The compiler expected a reference to a symbol at the location specified in the error message.

当你在类的 extends 子句中使用表达式时就会出现这个错误。

This error can occur if you use an expression in the extends clause of a class.

阶段 3：验证绑定表达式link

Phase 3: binding expression validationlink

在验证阶段，Angular 的模板编译器会使用 TypeScript 编译器来验证模板中的绑定表达式。 通过在项目的 tsconfig.json（参见 Angular Compiler Options）的 "angularCompilerOptions" 中添加编译选项 "fullTemplateTypeCheck" 可以启用这个阶段。

In the validation phase, the Angular template compiler uses the TypeScript compiler to validate the binding expressions in templates. Enable this phase explicitly by adding the compiler option "fullTemplateTypeCheck" in the "angularCompilerOptions" of the project's tsconfig.json (see Angular Compiler Options).

当模板绑定表达式中检测到类型错误时，进行模板验证时就会生成错误。这和 TypeScript 编译器在处理 .ts 文件中的代码时报告错误很相似。

Template validation produces error messages when a type error is detected in a template binding expression, similar to how type errors are reported by the TypeScript compiler against code in a .ts file.

比如，考虑下列组件：

For example, consider the following component:

      
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      @Component({
  selector: 'my-component',
  template: '{{person.addresss.street}}'
})
class MyComponent {
  person?: Person;
}
    

这会生成如下错误：

This will produce the following error:

      
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      my.component.ts.MyComponent.html(1,1): : Property 'addresss' does not exist on type 'Person'. Did you mean 'address'?
    

错误信息中汇报的文件名 my.component.ts.MyComponent.html 是一个由模板编译器生成出的合成文件， 用于保存 MyComponent 类的模板内容。 编译器永远不会把这个文件写入磁盘。这个例子中，这里的行号和列号都是相对于 MyComponent 的 @Component 注解中的模板字符串的。 如果组件使用 templateUrl 来代替 template，这些错误就会在 templateUrl 引用的 HTML 文件中汇报，而不是这个合成文件中。

The file name reported in the error message, my.component.ts.MyComponent.html, is a synthetic file generated by the template compiler that holds contents of the MyComponent class template. Compiler never writes this file to disk. The line and column numbers are relative to the template string in the @Component annotation of the class, MyComponent in this case. If a component uses templateUrl instead of template, the errors are reported in the HTML file referenced by the templateUrl instead of a synthetic file.

错误的位置是从包含出错的插值表达式的那个文本节点开始的。 如果错误是一个属性绑定，比如 [value]="person.address.street" ，错误的位置就是那个包含错误的属性的位置。

The error location is the beginning of the text node that contains the interpolation expression with the error. If the error is in an attribute binding such as [value]="person.address.street", the error location is the location of the attribute that contains the error.

这个验证过程使用 TypeScript 的类型检查器，这些选项也会提供给 TypeScript 编译器以控制类型验证的详细程度。 比如，如果指定了 strictTypeChecks，就会像上面的错误信息一样报告 my.component.ts.MyComponent.html(1,1): : Object is possibly 'undefined' 错误。

The validation uses the TypeScript type checker and the options supplied to the TypeScript compiler to control how detailed the type validation is. For example, if the strictTypeChecks is specified, the error my.component.ts.MyComponent.html(1,1): : Object is possibly 'undefined' is reported as well as the above error message.

类型窄化link

Type narrowinglink

在 ngIf 指令中使用的表达式用来在 Angular 模板编译器中窄化联合类型，就像 TypeScript 中的 if 表达式一样。 比如，要在上述模板中消除 Object is possibly 'undefined' 错误，可以把它改成只在 person 的值初始化过的时候才生成这个插值表达式。

The expression used in an ngIf directive is used to narrow type unions in the Angular template compiler, the same way the if expression does in TypeScript. For example, to avoid Object is possibly 'undefined' error in the template above, modify it to only emit the interpolation if the value of person is initialized as shown below:

      
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      @Component({
  selector: 'my-component',
  template: '<span *ngIf="person"> {{person.addresss.street}} </span>'
})
class MyComponent {
  person?: Person;
}
    

使用 *ngIf 能让 TypeScript 编译器推断出这个绑定表达式中使用的 person 永远不会是 undefined。

Using *ngIf allows the TypeScript compiler to infer that the person used in the binding expression will never be undefined.

类似于的 ngIf 的自定义指令link

Custom ngIf like directiveslink

那些行为与 *ngIf 类似的指令可以通过包含一个静态成员作为标记，来告诉模板编译器它们希望和 *ngIf 享受同等待遇。这个 *ngIf 的静态成员就是：

Directives that behave like *ngIf can declare that they want the same treatment by including a static member marker that is a signal to the template compiler to treat them like *ngIf. This static member for *ngIf is:

      
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      public static ngIfUseIfTypeGuard: void;
    

它声明了 NgIf 指令的 ngIf 属性应该在用到它的模板中看做一个守卫，以表明只有当 ngIf 这个输入属性为 true 时，才应该生成那个模板。

This declares that the input property ngIf of the NgIf directive should be treated as a guard to the use of its template, implying that the template will only be instantiated if the ngIf input property is true.

非空类型断言操作符link

Non-null type assertion operatorlink

使用 非空类型断言操作符可以在不方便使用 *ngIf 或 当组件中的某些约束可以确保这个绑定表达式在求值时永远不会为空时，防止出现 Object is possibly 'undefined' 错误。

Use the non-null type assertion operator to suppress the Object is possibly 'undefined' error when it is inconvenient to use *ngIf or when some constraint in the component ensures that the expression is always non-null when the binding expression is interpolated.

在下列例子中，person 和 address 属性总是一起出现的，如果 person 非空，则 address 也一定非空。没有一种简便的写法可以向 TypeScript 和模板编译器描述这种约束。但是这个例子中使用 address!.street 避免了报错。

In the following example, the person and address properties are always set together, implying that address is always non-null if person is non-null. There is no convenient way to describe this constraint to TypeScript and the template compiler, but the error is suppressed in the example by using address!.street.

      
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@Component({
  selector: 'my-component',
  template: '<span *ngIf="person"> {{person.name}} lives on {{address!.street}} </span>'
})
class MyComponent {
  person?: Person;
  address?: Address;
 
  setData(person: Person, address: Address) {
    this.person = person;
    this.address = address;
  }
}
    

应该保守点使用非空断言操作符，因为将来对组件的重构可能会破坏这个约束。

The non-null assertion operator should be used sparingly as refactoring of the component might break this constraint.

这个例子中，更建议在 *ngIf 中包含对 address 的检查，代码如下：

In this example it is recommended to include the checking of address in the *ngIfas shown below:

      
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@Component({
  selector: 'my-component',
  template: '<span *ngIf="person && address"> {{person.name}} lives on {{address.street}} </span>'
})
class MyComponent {
  person?: Person;
  address?: Address;
 
  setData(person: Person, address: Address) {
    this.person = person;
    this.address = address;
  }
}
    

使用 $any() 禁用类型检查link

Disabling type checking using $any()link

可以通过把绑定表达式包含在类型转换伪函数 $any() 中来禁用类型检查。 编译器会像在 TypeScript 中使用 <any> 或 as any 进行类型转换一样对待它。

Disable checking of a binding expression by surrounding the expression in a call to the $any() cast pseudo-function. The compiler treats it as a cast to the any type just like in TypeScript when a <any> or as any cast is used.

下面的例子中，通过把 person 转换成 any 类型，忽略了 Property addresss does not exist 错误。

In the following example, the error Property addresss does not exist is suppressed by casting person to the any type.

      
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      @Component({
  selector: 'my-component',
  template: '{{$any(person).addresss.street}}'
})
class MyComponent {
  person?: Person;
}
    

用 extends 语法配置继承方式link

Configuration inheritance with extendslink

像 TypeScript 编译器相似，Angular 编译器也支持在 tsconfig.json 的 angularCompilerOptions 中使用 extends 语法。 tsconfig 文件可以 使用 extends 属性从其它文件中继承配置。 extends 位于顶级，和 compilerOptions、angularCompilerOptions 同级。 首先加载 base 文件中的配置，然后用当前配置文件中的选项进行覆盖。比如：

Similar to TypeScript Compiler, Angular Compiler also supports extends in the tsconfig.json on angularCompilerOptions. A tsconfig file can inherit configurations from another file using the extends property. The extends is a top level property parallel to compilerOptions and angularCompilerOptions. The configuration from the base file are loaded first, then overridden by those in the inheriting config file. Example:

      
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{
  "extends": "../tsconfig.base.json",
  "compilerOptions": {
    "experimentalDecorators": true,
    ...
  },
  "angularCompilerOptions": {
    "fullTemplateTypeCheck": true,
    "preserveWhitespaces": true,
    ...
  }
}
    

关于 tsconfig extends 语法的更多知识，参见 TypeScript 手册。

More information about tsconfig extends can be found in the TypeScript Handbook.

Angular 模板编译器选项link

Angular template compiler optionslink

模板编译器的选项通过 tsconfig.json 文件中 "angularCompilerOptions" 对象的成员来指定。 给模板编译器的选项随着给 TypeScript 选项一起提供，如下所示：

The template compiler options are specified as members of the "angularCompilerOptions" object in the tsconfig.json file. Specify template compiler options along with the options supplied to the TypeScript compiler as shown here:

      
        content_copy
      
      {
    "compilerOptions": {
      "experimentalDecorators": true,
                ...
    },
    "angularCompilerOptions": {
      "fullTemplateTypeCheck": true,
      "preserveWhitespaces": true,
                ...
    }
}
    

下面的部分会讲解 Angular 模板编译器的选项。

The following section describes the Angular's template compiler options.

enableResourceInlininglink

该选项指示编译器将所有 @Component 装饰器中的 templateUrl 和 styleUrls 属性替换成内联在 template 和 styles 属性中的常量。 当启用时，ngc 输出的 .js 文件中就没有惰性加载的 templateUrl 或 styleUrls。

This option instructs the compiler to replace the templateUrl and styleUrls property in all @Component decorators with inlined contents in template and styles properties. When enabled, the .js output of ngc will have no lazy-loaded templateUrl or styleUrls.

skipMetadataEmitlink

该选项告诉编译器不要生成 .metadata.json 文件。默认为 false。

This option tells the compiler not to produce .metadata.json files. The option is false by default.

.metadata.json 文件中包含模板编译器需要从 .ts 文件中获取的信息，但它没有包含在由 TypeScript 编译器生成的 .d.ts 文件中。 比如，该信息包含注解的内容（比如组件的模板），TypeScript 会把它放进 .js 文件里，但不会放进 .d.ts 文件里。

.metadata.json files contain information needed by the template compiler from a .ts file that is not included in the .d.ts file produced by the TypeScript compiler. This information contains, for example, the content of annotations (such as a component's template), which TypeScript emits to the .js file but not to the .d.ts file.

如果你要使用 TypeScript 的 --outFile 选项，则该选项应该设置为 true，因为 TypeScript 的这种输出形式中没有包含元数据。不建议在 Angular 中使用 --outFile 选项。请改用像 webpack 这样的打包器。

This option should be set to true if you are using TypeScript's --outFile option, because the metadata files are not valid for this style of TypeScript output. It is not recommended to use --outFile with Angular. Use a bundler, such as webpack, instead.

当使用工厂摘要（factory summaries）时，该选项也可以设置为 true，因为工厂摘要包含了 .metadata.json 中那些信息的副本。

This option can also be set to true when using factory summaries because the factory summaries include a copy of the information that is in the .metadata.json file.

strictMetadataEmitlink

该选项告诉模板编译器，，当 "skipMetadataEmit" 为 false 时，就要向 .metadata.json 中报告一个错误。该选项默认为 false。只有当 "skipMetadataEmit" 为 false，而且 "skipTemplateCodeGen" 为 true 时才应该开启该选项。

This option tells the template compiler to report an error to the .metadata.json file if "skipMetadataEmit" is false. This option is false by default. This should only be used when "skipMetadataEmit" is false and "skipTemplateCodeGen" is true.

该选项是为了验证为生成 npm 包而产生的 .metadata.json 文件。这种验证是严格的，并且会报告元数据中的错误，以免当模板编译器使用它时再出错。你可以通过在某个导出符号的注释文档中使用 @dynamic 注释来暂时防止（suppress）该选项报告错误。

This option is intended to validate the .metadata.json files emitted for bundling with an npm package. The validation is strict and can emit errors for metadata that would never produce an error when used by the template compiler. You can choose to suppress the error emitted by this option for an exported symbol by including @dynamic in the comment documenting the symbol.

即使 .metadata.json 中包含错误，如果该元数据只是用来确定注解的内容，那么它仍然可能是有效的。 元数据收集器无法预知哪些符号是为了用作注解而设计的，所以它会先在导出符号的元数据中包含这些错误节点。然后，如果模板编译器真的用到了这些符号，它就能使用这个错误节点来报告错误。如果库的使用者想要在注解中使用某个符号，则直到客户代码使用了该符号时，模板编译器才会报告该错误。此选项能让你在库的构建阶段就检测出这类错误，比如，Angular 本身的这些库就是这么干的。

It is valid for .metadata.json files to contain errors. The template compiler reports these errors if the metadata is used to determine the contents of an annotation. The metadata collector cannot predict the symbols that are designed for use in an annotation, so it will preemptively include error nodes in the metadata for the exported symbols. The template compiler can then use the error nodes to report an error if these symbols are used. If the client of a library intends to use a symbol in an annotation, the template compiler will not normally report this until the client uses the symbol. This option allows detecting these errors during the build phase of the library and is used, for example, in producing Angular libraries themselves.

skipTemplateCodegenlink

该选项告诉编译器不要生成 .ngfactory.js 和 .ngstyle.js 文件。 如果设置了，则它会关闭大多数模板编译器，并禁止报告对模板的诊断信息。 该选项可用于指示模板编译器生成 .metadata.json 文件，以便作为 npm 包进行分发，同时，避免生成那些无法分发到 npm 的 .ngfactory.js 和 .ngstyle.js 文件。

This option tells the compiler to suppress emitting .ngfactory.js and .ngstyle.js files. When set, this turns off most of the template compiler and disables reporting template diagnostics. This option can be used to instruct the template compiler to produce .metadata.json files for distribution with an npm package while avoiding the production of .ngfactory.js and .ngstyle.js files that cannot be distributed to npm.

strictInjectionParameterslink

当设置为 true 时，该选项告诉编译器对那些无法确定类型的注入参数报错。 当不提供该选项或为 false 时，对于标记为 @Injectable 的类的构造函数中那些无法确定类型的参数将生成一个警告。

When set to true, this options tells the compiler to report an error for a parameter supplied whose injection type cannot be determined. When this option is not provided or is false, constructor parameters of classes marked with @Injectable whose type cannot be resolved will produce a warning.

注意：建议将此选项显式更改为 true，因为此选项将来将会默认为 true。

Note: It is recommended to change this option explicitly to true as this option will default to true in the future.

flatModuleOutFilelink

如果为 true，则该选项告诉模板编译器为指定的文件名生成一个扁平模块索引和相应的扁平模块元数据。当创建打包形式类似于 @angular/core 和 @angular/common 这样的扁平模块时，请使用该选项。 使用此选项，只会生成一个 .metadata.json 文件，其中包含从库索引中导出的符号所需的全部元数据。在生成的 .ngfactory.js 文件中，扁平模块索引用于导入所有符号，包括库索引中的公共 API，和那些受限的内部符号。

When set to true, this option tells the template compiler to generate a flat module index of the given file name and the corresponding flat module metadata. Use this option when creating flat modules that are packaged similarly to @angular/core and @angular/common. When this option is used, the package.json for the library should refer to the generated flat module index instead of the library index file. With this option only one .metadata.json file is produced, which contains all the metadata necessary for symbols exported from the library index. In the generated .ngfactory.js files, the flat module index is used to import symbols that includes both the public API from the library index as well as shrowded internal symbols.

默认情况下，files 字段中提供的 .ts 文件会被当做库索引。如果指定了多个 .ts 文件，则使用 libraryIndex 来选择要使用的索引文件。如果提供了多个 .ts 文件但没有指定 libraryIndex，就会产生错误。 编译器会用 flatModuleOutFile 所指定的名称在与库索引的 .d.ts 文件相同的位置创建平面模块索引的 .d.ts 和 .js 文件。比如，如果库使用 public_api.ts 文件作为模块的库索引，则 tsconfig.json 的 files 字段应该是 ["public_api.ts"]。 flatModuleOutFile。然后还可以将 flatModuleOutFile 选项设置为 index.js，它将会生成 index.d.ts 和 index.metadata.json 文件。这个库的 package.json 的 module 字段将会是 "inex.js"，而 typings 字段将会是 "index.d.ts"。

By default the .ts file supplied in the files field is assumed to be the library index. If more than one .ts file is specified, libraryIndex is used to select the file to use. If more than one .ts file is supplied without a libraryIndex, an error is produced. A flat module index .d.ts and .js will be created with the given flatModuleOutFile name in the same location as the library index .d.ts file. For example, if a library uses the public_api.ts file as the library index of the module, the tsconfig.json files field would be ["public_api.ts"]. The flatModuleOutFile options could then be set to, for example "index.js", which produces index.d.ts and index.metadata.json files. The library's package.json's module field would be "index.js" and the typings field would be "index.d.ts".

flatModuleIdlink

该选项可以指定用于导入平面模块的首选模块 ID。从平面模块中导入符号时，模板编译器所生成的引用将使用此模块名称。只有在同时提供了 flatModuleOutFile 选项时，该选项才有意义，否则编译器会忽略它。

This option specifies the preferred module id to use for importing a flat module. References generated by the template compiler will use this module name when importing symbols from the flat module. This is only meaningful when flatModuleOutFile is also supplied. Otherwise the compiler ignores this option.

generateCodeForLibrarieslink

该选项告诉模板编译器，为 .d.ts 文件生成与 .metadata.json 对应的工厂文件（.ngfactory.js 和 .ngstyle.js）。该选项默认为 true。如果为 false，则只会为 .ts 文件生成工厂文件。

This option tells the template compiler to generate factory files (.ngfactory.js and .ngstyle.js) for .d.ts files with a corresponding .metadata.json file. This option defaults to true. When this option is false, factory files are generated only for .ts files.

当使用工厂摘要（factory summaries）时，该选项应该设置为 false。

This option should be set to false when using factory summaries.

fullTemplateTypeChecklink

该选项告诉编译器，为模板编译器开启绑定表达式校验阶段，它使用 TypeScript 来验证各个绑定表达式。

This option tells the compiler to enable the binding expression validation phase of the template compiler which uses TypeScript to validate binding expressions.

该选项默认为 false。

This option is false by default.

注意：建议把它设置为 true，因为该选项将来会默认为 true。

Note: It is recommended to set this to true because this option will default to true in the future.

annotateForClosureCompilerlink

该选项会告诉编译器使用 Tsickle 来为所生成的 JavaScript 文件添加 JSDoc 注释，供 Closure Compiler 使用。该选项默认为 false。

This option tells the compiler to use Tsickle to annotate the emitted JavaScript with JSDoc comments needed by the Closure Compiler. This option defaults to false.

annotationsAslink

使用该选项可以修改 Angular 特有的注解的生成方式，以改善摇树优化。对非 Angular 的注解和装饰器无效。默认为 static fields

Use this option to modify how the Angular specific annotations are emitted to improve tree-shaking. Non-Angular annotations and decorators are unaffected. Default is static fields.

tracelink

这会告诉编译器在编译模板时打印出额外的信息。

This tells the compiler to print extra information while compiling templates.

enableLegacyTemplatelink

从 Angular 4.0 开始，不建议再使用 <template>，而是改用 <ng-template> 来避免与 DOM 中的同名元素发生冲突。把该选项设置为 true 可以让你继续使用已废弃的 <template> 元素。 该选项默认为 false。某些第三方 Angular 库可能需要此选项。

Use of the <template> element was deprecated starting in Angular 4.0 in favor of using <ng-template> to avoid colliding with the DOM's element of the same name. Setting this option to true enables the use of the deprecated <template> element. This option is false by default. This option might be required by some third-party Angular libraries.

disableExpressionLoweringlink

Angular 模板编译器会转换注解中用到或可能用到的代码，以允许从模板工厂模块中导入代码。详情参见元数据重写。

The Angular template compiler transforms code that is used, or could be used, in an annotation to allow it to be imported from template factory modules. See metadata rewriting for more information.

把该选项设置为 false 会禁用这种重写，必要时可以手动重写。

Setting this option to false disables this rewriting, requiring the rewriting to be done manually.

disableTypeScriptVersionChecklink

当为 true 时，该选项告诉编译器不要检查 TypeScript 的版本。 当时用了不支持的 TypeScript 版本时，该选项将会跳过检查，并且不会报错。 不建议把该选项设置为 true，因为不支持的 TypeScript 版本可能会带来未定义的行为。

When true, this option tells the compiler not to check the TypeScript version. The compiler will skip checking and will not error out when an unsupported version of TypeScript is used. Setting this option to true is not recommended because unsupported versions of TypeScript might have undefined behaviour.

该选项默认为 false。

This option is false by default.

preserveWhitespaceslink

该选项会告诉编译器是否要从已编译的模板中删除空白的文本节点（为 false 则删除）。从 v6 开始，该选项默认为 false，这会生成较小的模板工厂模块。

This option tells the compiler whether to remove blank text nodes from compiled templates. As of v6, this option is false by default, which results in smaller emitted template factory modules.

allowEmptyCodegenFileslink

告诉编译器生成所有可能生成的文件，即使它们是空的。默认情况下，该选项为 false。这是供 Bazel 构建规则使用的选项，用于简化 Bazel 规则跟踪文件依赖的方式。 建议不要在 Bazel 规则之外使用该选项。

Tells the compiler to generate all the possible generated files even if they are empty. This option is false by default. This is an option used by the Bazel build rules and is needed to simplify how Bazel rules track file dependencies. It is not recommended to use this option outside of the Bazel rules.