Angular2 FormArray -在页面上显示文本区字符数-如何？

import { Component } from '@angular/core';
import { FormArray, FormControl } from '@angular/forms';

@Component({
  selector: 'app-example',
  template: `
    <div formArrayName="textAreas">
      <div *ngFor="let control of textAreas.controls; let i = index">
        <textarea [formControlName]="i"></textarea>
        <p>Character count: {{ getCharacterCount(control.value) }}</p>
      </div>
    </div>
  `,
})
export class ExampleComponent {
  textAreas: FormArray;

  constructor() {
    this.textAreas = new FormArray([]);
  }

  getCharacterCount(value: string): number {
    return value.length;
  }
}