Answer by Rohit.007 for Angular: conditional class with *ngClass

In Angular 7.X

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.

<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>