Angular 6: How to change page background-color dynamically - css

Question

I work on an Angular 6 app (with Bootstrap 4) and need to change the page background color depending on which page the user enters. Default is white, but for login and registration screen the page color needs to be blue.
What I found so far:
in ngAfterViewInit() using
this.elementRef.nativeElement.ownerDocument: this approach makes the
app more vulnerable to XSS attacks and I want to avoid that.
Set View Encapsulation to None in app.component.ts: this way I can
set the body color in the app.component, that is 1 step forward.
So, now I have in my app.component.css:
body {
background-color: blue;
}
Question:
How can I change that color value (in app.component) using a variable?
With [ngStyle] I can not reach the body background-color.
Maybe using a css variable? but how can I change the value of that css variable dynamically?
I'm new to Sass, but might this offer a solution?
My question is different from the other question on this subject as I need to be able tochange the color value dynamically.

Answer 1

use render2 and set class to body using document object
app.component.ts
constructor(private renderer: Renderer2) {
this.renderer.addClass(document.body, 'body-class');
}
Note: if you are toggling classes, just remove previous class before assigning new class

Answer 2

The way I would do it is based on the routes. When defining the routes, you can add extra data, for example a class name.
When the route changes (i.e. via navigation), the data from the active route can be used to set the class on the body tag.
This is how you can achieve this
Update the styles.css to add different classes for body:
body {
...
}
body.red {
background-color: #ff8181;
}
body.blue {
background-color: #a0c3ee;
}
Update the routes to add extra data, specifying the body class name. Add an extra data property, like bodyClass:
const routes: Routes = [
{ path: '', component: DefaultComponent },
{ path: 'red', component: RedComponent, data: { bodyClass: 'red' } },
{ path: 'blue', component: BlueComponent, data: { bodyClass: 'blue' } }
];
Write the code to read the bodyClass and set the class to the body element when navigation occurs. This can be done in the app.component.ts:
#Component({
selector: 'app-root',
template: `
<div>
<router-outlet></router-outlet>
<app-menu></app-menu>
</div>
`
})
export class AppComponent implements OnInit {
constructor(
#Inject(DOCUMENT) private document,
private renderer: Renderer2,
private router: Router,
private activatedRoute: ActivatedRoute) {
}
ngOnInit() {
this.router.events
.pipe(filter((event) => event instanceof NavigationEnd))
.pipe(map(() => this.activatedRoute))
.pipe(map((route) => {
while (route.firstChild) {
route = route.firstChild;
}
return route;
}))
.pipe(filter((route) => route.outlet === 'primary'))
.pipe(mergeMap((route) => route.data))
.subscribe((event) => this.updateBodyClass(event.bodyClass));
}
private updateBodyClass(customBodyClass?: string) {
this.renderer.setAttribute(this.document?.body, 'class', '');
if (customBodyClass) {
this.renderer.addClass(this.document?.body, customBodyClass);
}
}
}
Here is a demo on StackBlitz: https://stackblitz.com/edit/angular-ivy-rs1tai

Answer 3

Why not just define a separate class based on different background-color? For instance:
.blue {
background: blue
}
.green {
background: green
}
.grey {
background: grey
}
And then set these classes on the body using ng-class or ngClass whatever convention you use based on the page. This should be fairly easy to implement.

Answer 4

My favourite approach for doing stuff like this is to add a class to html tag depending on the route. For example, we have some code in our basic layout component (you could put it in your root component) that does this inside ngOnInit:
let wrapper = ''
const path = this.activatedRoute.snapshot.routeConfig.path
wrapper += this.tidyPath(path)
if (wrapper !== '') wrapper += '-'
const childPath = this.activatedRoute.snapshot.firstChild.routeConfig.path
wrapper += this.tidyPath(childPath)
this.routeWrapperCssClass = wrapper
$('html').addClass(this.routeWrapperCssClass)
This will add a class to your html tag to make it look like this (although you may have to tweak this code to suit your app):
<html class="registration">
....
</html>
The class will be instantly updated whenever you change route.
Now you can do this in your main stylesheet:
body {
background-color: pink;
}
html.registration body {
background-color: yellow;
}
You could also do things like hide elements based on the class added to the html tag like so:
.navbar {
display: block;
}
html.registration .navbar {
display: none;
}
Because you know what route you are on at all times you have total control via CSS.
PS you may want to use render2 instead of jQuery to do the DOM manipulation - see this article ... https://alligator.io/angular/using-renderer2 ... never used it myself before but almost identical to jQuery syntax - thanks to Pratap A.K answer for this

Answer 5

Personally i replace :
<body>
<app-root></app-root>
</body>
to
<app-root></app-root>
and then i add all the time the body on components or if i have multi
router-outlets i add it on app.component.css