Passing Optional Parameters to a Route

Query parameters allow you to pass optional parameters to a route such as pagination information.
For example, on a route with a paginated list, the URL might look like the following to indicate that we've loaded the second page:
localhost:3000/product-list?page=2
The key difference between query parameters and route parameters is that route parameters are essential to determining route, whereas query parameters are optional.
Passing Query Parameters
Use the [queryParams] directive along with [routerLink] to pass query parameters. For example:
<a [routerLink]="['product-list']" [queryParams]="{ page: 99 }">Go to Page 99</a>
Alternatively, we can navigate programmatically using the Router service:
  goToPage(pageNum) {
    this.router.navigate(['/product-list'], { queryParams: { page: pageNum } });
  }
Reading Query Parameters
Similar to reading route parameters, the Router service returns an Observable we can subscribe to to read the query parameters:
import { Component } from '@angular/core';
import { ActivatedRoute, Router } from '@angular/router';
​
@Component({
  selector: 'product-list',
  template: `<!-- Show product list -->`
})
export default class ProductList {
  constructor(
    private route: ActivatedRoute,
    private router: Router) {}
​
  ngOnInit() {
    this.sub = this.route
      .queryParams
      .subscribe(params => {
        // Defaults to 0 if no query param provided.
        this.page = +params['page'] || 0;
      });
  }
​
  ngOnDestroy() {
    this.sub.unsubscribe();
  }
​
  nextPage() {
    this.router.navigate(['product-list'], { queryParams: { page: this.page + 1 } });
  }
}
​View Example​
​See Official Documentation on Query Parameters​
Controlling Access to or from a Route
Using Auxiliary Routes
Last updated 1 year ago