Angular2 - Starter - Pipes, Custom Pipes

在Angular2 模板中，我们在显示数据时，可以使用通道将数据转换成相应的格式的值的形式来显示，而且这不改变源数据。比如，我们可以使用date通道来转换时间显示的格式： {{date | date:'yyyy-MM-dd'}} ,(1) 以下是Angular提供的基本的通道.

Basic Pipes

Pipe Name	Usage	Parameters or Effection
currency	{{test.currency | currency }}	1234569678 > USD1,234,569,678.00
date	{{test.date | date:'yyyy-MM-dd'}}	date:'mediumDate',//Jan,9,2017 date:'shortTime',//9:36 pm
json	{{test.json | json }}	[object Object] > { "name": "test", "title": "Test Pipes" } //with json pipe
uppercase	{{test.str | uppercase }}	hello pipes > HELLO PIPES
lowercase	{{test.str1 | lowercase }}	Hello > hello
percent	{{test.percent | percent:'.3' }}	percent:'.3'//0.25 > 25.000%
number	{{test.decimal | number:'5.1-2' }}	number:'5.1-3'//23440.0987 > 23,440.099

(2) 以下自定义了一转换电话号码指定数位尾号之外的数字的Pipe, +008615527370515 > ***********70515

//tail-number-length.pipe.ts
import { Pipe,PipeTransform } from '@angular/core';

@Pipe({
//通道名称
  name:'tailNumberLength',
  pure:false
})
export class TailNumberLengthPipe implements PipeTransform{
  transform(value: string, length:number): any {
//对源数据的转换方法
    let tailNumberLength = (length === undefined ? 4 : length);
    let prefixLength = value.length - tailNumberLength;
    let target = '';
    for(let index = 0;index < prefixLength; ++index){
      target += '*';
    }
    target += value.substr(prefixLength);
    return target;
  }
}

　　

//tail-number-length.module.ts
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { TailNumberLengthPipe } from './tail-number-length.pipe';

构建一个NgModule装饰的TailNumberPipeModule
@NgModule({
  declarations:[
//引入TailNumberLengthPipe
    TailNumberLengthPipe
  ],
  imports:[
    CommonModule
  ],
  exports:[
    TailNumberLengthPipe
  ]
})

export class TailNumberPipeModule{};

appComponent.module.ts
@NgModule({
  bootstrap: [ AppComponent ],
  imports: [
 // import custom modules
    TailNumberPipeModule
]
})

{{person.phone | tailNumberLength:5}}//+008615527370515 > ***********70515