You can do this by simply using ngClass :

Here first,second and third are the name of the classes.

And instead of true/false , you can directly put your conditions over there

 <div [ngClass]="{'first': true, 'second': true, 'third': false}">...</div>

In your case

 <div [ngClass]="{'loading-state': loading, 'my-class': loading }">...</div>

Or Shorter Veriosn (as @matko.kvesic commented)

<div [ngClass]="{'loading-state my-class': loading}">...</div>

Although Vivek Doshi answer is totally correct, below I put other alternatives to do the same with different boolean variables:

1st Solution: [class.className]

Template:

<div [class.first-class]="addFirst" [class.second-class]="addSecond">...</div>

Component:

export class MyComponent {
  ...
  addFirst: boolean;
  addSecond: boolean;
  ...
}

2nd Solution: [ngClass] with method binding

Template:

<div [ngClass]="setClasses()">...</div>

Component:

export class MyComponent {
  ...
  addFirst: boolean;
  addSecond: boolean;
  ...
  setClasses() {
    return {
      'first-class': this.addFirst,
      'second-class': this.addSecond
    };
  }
  ...
}

Last solution, but not least:

Template:

<div [ngClass]="{'first-class': addFirst, 'second-class': addSecond}">...</div>

Component:

export class MyComponent {
  ...
  addFirst: boolean;
  addSecond: boolean;
  ...
}