NgClass

A class binding is a good way to add or remove a single class.

To add or remove many CSS classes at the same time, the NgClass directive may be the better choice.

Try binding ngClass to a key:value control object. Each key of the object is a CSS class name; its value is true if the class should be added, false if it should be removed.

currentClasses: {};
setCurrentClasses() {
  // CSS classes: added/removed per current state of component properties
  this.currentClasses =  {
    'saveable': this.canSave,
    'modified': !this.isUnchanged,
    'special':  this.isSpecial
  };
}

<div [ngClass]="currentClasses">This div is initially saveable, unchanged, and special</div>