[Angular] ngClass conditional

Using ngClass for conditional styling, here is the usage from the docs:

/**
 * @ngModule CommonModule
 *
 * @usageNotes
 * ```
 *     <some-element [ngClass]="'first second'">...</some-element>
 *
 *     <some-element [ngClass]="['first', 'second']">...</some-element>
 *
 *     <some-element [ngClass]="{'first': true, 'second': true, 'third': false}">...</some-element>
 *
 *     <some-element [ngClass]="stringExp|arrayExp|objExp">...</some-element>
 *
 *     <some-element [ngClass]="{'class1 class2 class3' : true}">...</some-element>
 * ```
 *
 * @description
 *
 * Adds and removes CSS classes on an HTML element.
 *
 * The CSS classes are updated as follows, depending on the type of the expression evaluation:
 * - `string` - the CSS classes listed in the string (space delimited) are added,
 * - `Array` - the CSS classes declared as Array elements are added,
 * - `Object` - keys are CSS classes that get added when the expression given in the value
 *              evaluates to a truthy value, otherwise they are removed.
 *
 * @publicApi
 */

 

It is also recommended when the conditional logics is complicated, we can using Function:

<div [ngClass]="getCondClass(i)" *ngFor="let item of items as collection; index as i; first as isFirst; last as isLast; even as isEven; odd as isOdd;">
  {{i + 1}}: {{item}} -- {{collection}}
</div>

  getCondClass (index) {
    if (index + 1 === 3) {
      // Using array to add 'third', 'very*important' classes
      return ['third', 'very-important'];
    }

    if (index === this.items.length - 1) {
      // Using string to add class
      return 'last';
    }

    if (index === 0) {
      // Using object to add class
      return {'first': true};
    }
  }