angular - How can I add a class to an element on hover?

Question

How to add class to a div when hovered on the div.

Template -

<div class="red">On hover add class ".yellow"</div>

Component -

import {Component} from 'angular2/core';

@Component({
  selector: 'hello-world',
  templateUrl: 'src/hello_world.html',
  styles: [`
    .red {
      background: red;
    }

    .yellow {
      background: yellow;
    }

  `]
})
export class HelloWorld {
}

Demo

[ NOTE - I specifically want to add a new class and not modify the existing classes ]

Sigh! It is such a normal use case and I do not see any straight forward solution yet!

Answer 1

Not to dirty the code I just coded simple hover-class directive.

<span hover-class="btn-primary" class="btn" >Test Me</span>

Running Sample

Code Editor stackblitz

Here below the directive,

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

@Directive({
  selector: '[hover-class]'
})
export class HoverClassDirective {

  constructor(public elementRef:ElementRef) { }
  @Input('hover-class') hoverClass:any;  

  @HostListener('mouseenter') onMouseEnter() {
    this.elementRef.nativeElement.classList.add(this.hoverClass);
 }

  @HostListener('mouseleave') onMouseLeave() {
    this.elementRef.nativeElement.classList.remove(this.hoverClass);
  }

}