Passing Optional Parameters

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