提供一组内置验证器，可用于各种表单控件。
Provides a set of built-in validators that can be used by form controls.
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说明 验证器就是一个函数，它可以处理单个 FormControl
A validator is a function that processes a FormControl
静态方法 此验证器要求控件的值大于或等于指定的数字。 它只有函数形式，没有指令形式。
Validator that requires the control's value to be greater than or equal to the provided number. The validator exists only as a function and not as a directive.
static min (min: number): ValidatorFn
static min ( min : number ): ValidatorFn 参数 返回值 如果验证失败，则此验证器函数返回一个带有 min 属性的映射表（map），否则为 null。
ValidatorFn min property if the validation check fails, otherwise null.
使用说明 验证至少为 3 Validate against a minimum of 3 const control = new
FormControl (2, Validators.min(3)); console.log(control.errors); // {min: {min: 3, actual: 2}}
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const control = new FormControl ( 2 , Validators . min ( 3 ));
console . log ( control . errors ); // {min: {min: 3, actual: 2}}
此验证器要求控件的值小于等于指定的数字。 它只有函数形式，没有指令形式。
Validator that requires the control's value to be less than or equal to the provided number. The validator exists only as a function and not as a directive.
static max (max: number): ValidatorFn
static max ( max : number ): ValidatorFn 参数 返回值 如果验证失败，则此验证器函数返回一个带有 max 属性的映射表（map），否则为 null。
ValidatorFn max property if the validation check fails, otherwise null.
使用说明 验证最大为 15 Validate against a maximum of 15 const control = new
FormControl (16, Validators.max(15)); console.log(control.errors); // {max: {max: 15, actual: 16}}
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const control = new FormControl ( 16 , Validators . max ( 15 ));
console . log ( control . errors ); // {max: {max: 15, actual: 16}}
此验证器要求控件具有非空值。
Validator that requires the control have a non-empty value.
static required (control: AbstractControl): ValidationErrors | null
static required ( control : AbstractControl ): ValidationErrors | null 参数 返回值 如果验证失败，则此验证器函数返回一个带有 required 属性的映射表（map），否则为 null。
ValidationErrors | nullrequired property if the validation check fails, otherwise null.
使用说明 验证该字段不是空的 Validate that the field is non-empty const control = new
FormControl ('', Validators.required); console.log(control.errors); // {required: true}
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const control = new FormControl ( '' , Validators . required );
console . log ( control . errors ); // {required: true}
此验证器要求控件的值为真。它通常用来验证检查框。
Validator that requires the control's value be true. This validator is commonly used for required checkboxes.
static requiredTrue (control: AbstractControl): ValidationErrors | null
static requiredTrue ( control : AbstractControl ): ValidationErrors | null 参数 返回值 如果验证失败，则此验证器函数返回一个带有 required 属性、值为 true 的映射表（map），否则为 null。
ValidationErrors | nullrequired property set to true if the validation check fails, otherwise null.
使用说明 验证字段值为真 Validate that the field value is true const control = new
FormControl ('', Validators.requiredTrue); console.log(control.errors); // {required: true}
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const control = new FormControl ( '' , Validators . requiredTrue );
console . log ( control . errors ); // {required: true}
此验证器要求控件的值能通过 email 格式验证。
Validator that requires the control's value pass an email validation test.
static email (control: AbstractControl): ValidationErrors | null
static email ( control : AbstractControl ): ValidationErrors | null 参数 返回值 如果验证失败，则此验证器函数返回一个带有 email null。
ValidationErrors | nullemail null.
使用说明 验证该字段匹配有效的 email 格式。 Validate that the field matches a valid email pattern const control = new
FormControl ('bad@', Validators.email); console.log(control.errors); // {
email : true}
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const control = new FormControl ( 'bad@' , Validators . email );
console . log ( control . errors ); // { email : true}
此验证器要求控件值的长度大于等于所指定的最小长度。当使用 HTML5 的 minlength
Validator that requires the length of the control's value to be greater than or equal to the provided minimum length. This validator is also provided by default if you use the the HTML5 minlength
static minLength (minLength: number): ValidatorFn
static minLength ( minLength : number ): ValidatorFn 参数 返回值 如果验证失败，则此验证器函数返回一个带有 minlength null。
ValidatorFn minlength null.
使用说明 验证该字段至少有 3 个字符 Validate that the field has a minimum of 3 characters const control = new
FormControl ('ng', Validators.minLength(3)); console.log(control.errors); // {
minlength : {requiredLength: 3, actualLength: 2}}
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const control = new FormControl ( 'ng' , Validators . minLength ( 3 ));
console . log ( control . errors ); // { minlength : {requiredLength: 3, actualLength: 2}}
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<input minlength = "5" >
此验证器要求控件值的长度小于等于所指定的最大长度。当使用 HTML5 的 maxlength
Validator that requires the length of the control's value to be less than or equal to the provided maximum length. This validator is also provided by default if you use the the HTML5 maxlength
static maxLength (maxLength: number): ValidatorFn
static maxLength ( maxLength : number ): ValidatorFn 参数 返回值 如果验证失败，则此验证器函数返回一个带有 maxlength null。
ValidatorFn maxlength null.
使用说明 验证该字段最多具有 5 个字符 Validate that the field has maximum of 5 characters const control = new
FormControl ('Angular', Validators.maxLength(5)); console.log(control.errors); // {
maxlength : {requiredLength: 5, actualLength: 7}}
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const control = new FormControl ( 'Angular' , Validators . maxLength ( 5 ));
console . log ( control . errors ); // { maxlength : {requiredLength: 5, actualLength: 7}}
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<input maxlength = "5" >
此验证器要求控件的值匹配某个正则表达式。当使用 HTML5 的 pattern
Validator that requires the control's value to match a regex pattern. This validator is also provided by default if you use the HTML5 pattern
static pattern ( pattern : string | RegExp ): ValidatorFn 参数 返回值 如果验证失败，则此验证器函数返回一个带有 pattern null。
ValidatorFn pattern null.
注意，如果提供了 Regexp，则使用 Regexp 来测试值。另一方面，如果传给它一个字符串，则会自动添加 ^ 前缀和 $ 后缀（如果没有）， 并使用所生成的正则表达式来测试那些值。
Note that if a Regexp is provided, the Regexp is used as is to test the values. On the other hand, if a string is passed, the ^ character is prepended and the $ character is appended to the provided string (if not already present), and the resulting regular expression is used to test the values.
使用说明 验证该字段只包含字母或空格 Validate that the field only contains letters or spaces const control = new
FormControl ('1', Validators.pattern('[a-zA-Z ]*')); console.log(control.errors); // {
pattern : {requiredPattern: '^[a-zA-Z ]*$', actualValue: '1'}}
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const control = new FormControl ( '1' , Validators . pattern ( '[a-zA-Z ]*' ));
console . log ( control . errors ); // { pattern : {requiredPattern: '^[a-zA-Z ]*$', actualValue: '1'}}
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<input pattern = "[a-zA-Z ]*" >
此验证器什么也不做。
Validator that performs no operation.
static nullValidator (control: AbstractControl): ValidationErrors | null
static nullValidator ( control : AbstractControl ): ValidationErrors | null 参数 返回值 ValidationErrors | null
把多个验证器合并成一个函数，它会返回指定控件的各个错误映射表的并集。
Compose multiple validators into a single function that returns the union of the individual error maps for the provided control.
static compose (validators: null): null
static compose ( validators : null ): null 参数 返回值 如果验证失败，则此验证器函数返回各个验证器所返回错误对象的一个并集，否则为 null。
null: A validator function that returns an error map with the merged error maps of the validators if the validation check fails, otherwise null.
static compose (validators: ValidatorFn[]): ValidatorFn | null
static compose ( validators : ValidatorFn []): ValidatorFn | null 参数 返回值 ValidatorFn | null
把多个异步验证器合并成一个函数，它会返回指定控件的各个错误映射表的并集。
Compose multiple async validators into a single function that returns the union of the individual error objects for the provided control.
static composeAsync (validators: AsyncValidatorFn[]): AsyncValidatorFn | null
static composeAsync ( validators : AsyncValidatorFn []): AsyncValidatorFn | null 参数 返回值 如果验证失败，则此验证器函数返回各异步验证器所返回错误对象的一个并集，否则为 null。
AsyncValidatorFn | nullnull.
