Add class to body on Angular2

1. If part of your application is in Angular, then you can do this:

let body = document.getElementsByTagName('body')[0];
body.classList.remove("className");   //remove the class
body.classList.add("className");   //add the class

2. I'll prefer answer given by @Yurzui if the whole frontend is in Angular.

Angular2 doesn't provide any built in way to modify DOM elements outside the root component (except the <title>).

querySelector('body').classList.add('signin-page');
querySelector('body').classList.remove('signin-page');

or

@Component(
  selector: 'body',
  templateUrl: 'app_element.html'
)
class AppElement {
  @HostBinding('class.fixed') 
  bool isFixed = true;
}

See also

• How do I add a class to a given element?
• Angular 2.x bind class on body tag

You can change your root selector to body and then use HostBinding decorator

@Component({
  selector: 'body',
  template: `<child></child>`
})
export class AppComponent {
  @HostBinding('class') public cssClass = 'class1';
}

@Component({
  selector: 'child',
  template: `<button (click)="setClass()">Set class</button>`
})
export class ChildComponent {
  constructor(private rootComp: AppComponent) {  }
  setClass() {
    this.rootComp.cssClass = 'class2';
  }
}