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Angular 2 Directives


  • <input [value]="value"> - Binds attribute value class member name.

  • <div []="note"> - Binds attribute data-note to variable note.

  • <p green></p> - Custom directive


The main source of information about Angular 2 directives is the official documentation

Attribute directive

<div []="isActive"></div>

<span [style.color]="'red'"></span>

<p []="'This is value for data-note attribute'">A lot of text here</p>

Component is a directive with template

import { Component } from '@angular/core';
  selector: 'my-app',
  template: `
    <h1>Angular 2 App</h1>
    <p>Component is directive with template</p>
export class AppComponent {

Structural directives

<div *ngFor="let item of items">{{ item.description }}</div>

<span *ngIf="isVisible"></span>

Custom directive

import {Directive, ElementRef, Renderer} from '@angular/core';

  selector: '[green]',

class GreenDirective {
  constructor(private _elementRef: ElementRef, 
              private _renderer: Renderer) {
    _renderer.setElementStyle(_elementRef.nativeElement, 'color', 'green');


<p green>A lot of green text here</p>



import { Component } from '@angular/core';

// Defines example component and associated template
    selector: 'example',
    template: `
      <div *ngFor="let f of fruit"> {{f}} </div>
      <select required>
        <option *ngFor="let f of fruit" [value]="f"> {{f}} </option>

// Create a class for all functions, objects, and variables
export class ExampleComponent { 
    // Array of fruit to be iterated by *ngFor
    fruit = ['Apples', 'Oranges', 'Bananas', 'Limes', 'Lemons'];


<select required>
  <option value="Apples">Apples</option>
  <option value="Oranges">Oranges</option>
  <option value="Bananas">Bananas</option>
  <option value="Limes">Limes</option>
  <option value="Lemons">Lemons</option>

In its most simple form, *ngFor has two parts : let variableName of object/array

In the case of fruit = ['Apples', 'Oranges', 'Bananas', 'Limes', 'Lemons'];,

Apples, Oranges, and so on are the values inside the array fruit.

[value]="f" will be equal to each current fruit (f) that *ngFor has iterated over.

Unlike AngularJS, Angular2 has not continued with the use of ng-options for <select> and ng-repeat for all other general repetitions.

*ngFor is very similar to ng-repeat with slightly varied syntax.


Angular2 | Displaying Data

Angular2 | ngFor

Angular2 | Forms

Copy to Clipboard directive

In this example we are going to create a directive to copy a text into the clipboard by clicking on an element


import {
} from "@angular/core";

    selector: '[text-copy]'
export class TextCopyDirective {

    // Parse attribute value into a 'text' variable
    @Input('text-copy') text:string;

    constructor() {

    // The HostListener will listen to click events and run the below function, the HostListener supports other standard events such as mouseenter, mouseleave etc.
    @HostListener('click') copyText() {

        // We need to create a dummy textarea with the text to be copied in the DOM
        var textArea = document.createElement("textarea");

        // Hide the textarea from actually showing = 'fixed'; = '-999px'; = '-999px'; = '2em'; = '2em'; = '0'; = 'none'; = 'none'; = 'none'; = 'transparent';

        // Set the texarea's content to our value defined in our [text-copy] attribute
        textArea.value = this.text;

        // This will select the textarea;

        try {
            // Most modern browsers support execCommand('copy'|'cut'|'paste'), if it doesn't it should throw an error
            var successful = document.execCommand('copy');
            var msg = successful ? 'successful' : 'unsuccessful';
            // Let the user know the text has been copied, e.g toast, alert etc.
        } catch (err) {
            // Tell the user copying is not supported and give alternative, e.g alert window with the text to copy
            console.log('unable to copy');

        // Finally we remove the textarea from the DOM

export const TEXT_COPY_DIRECTIVES = [TextCopyDirective];


Remember to inject TEXT_COPY_DIRECTIVES into the directives array of your component

    <!-- Insert variable as the attribute's value, let textToBeCopied = '' -->
    <button [text-copy]="textToBeCopied">Copy URL</button>
    <button [text-copy]="''">Copy URL</button>

Testing a custom directive

Given a directive that highlights text on mouse events

import { Directive, ElementRef, HostListener, Input } from '@angular/core';

@Directive({ selector: '[appHighlight]' })
export class HighlightDirective {
  @Input('appHighlight') // tslint:disable-line no-input-rename
  highlightColor: string;

  constructor(private el: ElementRef) { }

  onMouseEnter() {
    this.highlight(this.highlightColor || 'red');

  onMouseLeave() {

  private highlight(color: string) { = color;

It can be tested like this

import { ComponentFixture, ComponentFixtureAutoDetect, TestBed } from '@angular/core/testing';

import { Component } from '@angular/core';
import { HighlightDirective } from './highlight.directive';

  selector: 'app-test-container',
  template: `
      <span id="red" appHighlight>red text</span>
      <span id="green" [appHighlight]="'green'">green text</span>
      <span id="no">no color</span>
class ContainerComponent { }

const mouseEvents = {
  get enter() {
    const mouseenter = document.createEvent('MouseEvent');
    mouseenter.initEvent('mouseenter', true, true);
    return mouseenter;
  get leave() {
    const mouseleave = document.createEvent('MouseEvent');
    mouseleave.initEvent('mouseleave', true, true);
    return mouseleave;

describe('HighlightDirective', () => {
  let fixture: ComponentFixture<ContainerComponent>;
  let container: ContainerComponent;
  let element: HTMLElement;

  beforeEach(() => {
      declarations: [ContainerComponent, HighlightDirective],
      providers: [
        { provide: ComponentFixtureAutoDetect, useValue: true },

    fixture = TestBed.createComponent(ContainerComponent);
    // fixture.detectChanges(); // without the provider
    container = fixture.componentInstance;
    element = fixture.nativeElement;

  it('should set background-color to empty when mouse leaves with directive without arguments', () => {
    const targetElement = <HTMLSpanElement>element.querySelector('#red');


  it('should set background-color to empty when mouse leaves with directive with arguments', () => {
    const targetElement = <HTMLSpanElement>element.querySelector('#green');


  it('should set background-color red with no args passed', () => {
    const targetElement = <HTMLSpanElement>element.querySelector('#red');


  it('should set background-color green when passing green parameter', () => {
    const targetElement = <HTMLSpanElement>element.querySelector('#green');


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