Angular2实现自定义双向绑定属性

import { Component, OnInit, Output, Input, EventEmitter } from '@angular/core';

@Component({
  selector: 'twoway',
  template: `
    <input [(ngModel)]="username">
    <p>Hello {{username}}!</p>
  `
})
export class TwoWayComponent implements OnInit {
  constructor() { }

  usernameValue: string;
  @Output() usernameChange = new EventEmitter();

  @Input()
  get username() {
    return this.usernameValue;
  }
  set username(val) {
    this.usernameValue = val;
    this.usernameChange.emit(this.usernameValue);
  }

  ngOnInit() {

  }
}