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Create a Simple Breadcrumb in Angular

December 14, 2018

Recently, I am building an enterprise resource planning (ERP) platform for my company. The system is required to be flexible to hold different individual modules. In this platform, user navigation should be clear and concise so that the users would conveniently know what location they are at while performing tasks on the platforms.

For example, a hierarchy like Dashboard -> IT HelpDesk -> Issue Log -> New can be provided as a reference of locations. And most importantly, users can navigate back to different level of pages conveniently. So I built a breadcrumb component to cater that need.

Demo for static link: Breadcrumb

Demo for dynamic link (123 is a dynamic ID): Breadcrumb

Configure the Routes

Af first, you need to configure your route correctly.

Take Dashboard -> IT HelpDesk -> Issue Log -> New as an example. Below code snippet shows a basic route structure.

{ path: '', component: LoginComponent, }, { path: 'dashboard', component: DashboardComponent, children: [ { path: 'it-helpdesk', component: ItHelpdeskComponent, children: [ { path: 'issue-log', children: [ { path: '', component: IssueLogListComponent }, { path: 'new', component: IssueLogDetailComponent }, { path: ':id', component: IssueLogDetailComponent } ] } ] } ] }

In order to use breadcrumb, we need to get their names from this route configuration, as in issue-log route is represented as Issue Log in the breadcrumb. Then we use data attribute in Route to store its display names. Hence, we modify the route configuration as below.

{ path: '', component: LoginComponent, }, { path: 'dashboard', component: DashboardComponent, data: { breadcrumb: 'Dashboard', }, children: [ { path: 'it-helpdesk', component: ItHelpdeskComponent, data: { breadcrumb: 'IT Helpdesk' }, children: [ { path: 'issue-log', data: { breadcrumb: 'Issue Log' }, children: [ { path: '', component: IssueLogListComponent }, { path: 'new', component: IssueLogDetailComponent, data: { breadcrumb: 'New' } }, { path: ':id', component: IssueLogDetailComponent, data: { breadcrumb: '' } } ] }, ] } ] }

Notice that the route issue-log/:id has no breadcrumb data yet. That is because this route contains dynamic parameters. We will automate the display text later when building the breadcrumb.

Breadcrumb Component

HTML

The HTML part is rather simple. Just use ol and li to list out all the breadcrumbs with *ngFor

breadcrumb.component.html

<ol class="breadcrumb"> <li *ngFor="let breadcrumb of breadcrumbs"> <span [routerLink]="breadcrumb.url" routerLinkActive="router-link-active"> {{ breadcrumb.label }} </span> </li> </ol>

SCSS

The CSS is not complicated either. Take note that when a breadcrumb is hovered, it should be dimmed.

breadcrumb.component.scss

.breadcrumb { background: none; font-size: 0.8em; margin: 0; a, span { color: darkgrey; } a:hover, span:hover { color: dimgrey; text-decoration: none; } li { list-style: none; float: left; margin: 5px; } li:last-child { margin-right: 20px; } li::after { content: "->"; color: darkgrey; } li:last-child::after { content: ""; } }

TypeScript

The most important part is the TypeScript part.

Interface

The first thing to do is to create an interface to standardize the data structure of a breadcrumb.

breadcrumb.interface.ts

export interface IBreadCrumb { label: string; url: string; }

Component

Then we can start to build our breadcrumb component. The basic code structures are as below.

import { Component, OnInit } from '@angular/core'; import { ActivatedRoute, Router, NavigationEnd } from '@angular/router'; import { IBreadCrumb } from '../../../interfaces/breadcrumb.interface'; import { filter, distinctUntilChanged } from 'rxjs/operators'; @Component({ selector: 'app-breadcrumb', templateUrl: './breadcrumb.component.html', styleUrls: ['./breadcrumb.component.scss'] }) export class BreadcrumbComponent implements OnInit { public breadcrumbs: IBreadCrumb[] constructor( private router: Router, private activatedRoute: ActivatedRoute, ) { this.breadcrumbs = this.buildBreadCrumb(this.activatedRoute.root); } ngOnInit() { // ... implementation of ngOnInit } /** * Recursively build breadcrumb according to activated route. * @param route * @param url * @param breadcrumbs */ buildBreadCrumb(route: ActivatedRoute, url: string = '', breadcrumbs: IBreadCrumb[] = []): IBreadCrumb[] { // ... implementation of buildBreadCrumb } }

As you can see, we have 2 functions need to be implemented.

ngOnInit() is the function triggered right when the component is created. In this function, we will get the current route and start to build breadcrumb from its root.

buildBreadCrumb() is the function we actually build a breadcrumb. It’s a recursive function to recursively loop the child of route object from the root to leaf, such as Dashboard all the way to Issue Log.

buildBreadCrumb()

  1. Label and Path First, let’s get the label and path of a single breadcrumb. Note that routeConfig could be null if the current route is on the root. Therefore, it must be checked before assign route.routeConfig.data.breadcrumb and route.routeConfig.path to variables, otherwise, exceptions will be thrown.
let label = route.routeConfig && route.routeConfig.data ? route.routeConfig.data.breadcrumb : ""; let path = route.routeConfig && route.routeConfig.data ? route.routeConfig.path : "";
  1. Handling Dynamic Parameters Second, we need to handle dynamic route such as :id. Take a look at this route.
{ path: 'issue-log/:id', component: IssueLogDetailComponent data: { breadcrumb: '' } }

The breadcrumb is previously left blank because the route is dynamic. I can only know the ID at runtime.

The activated route contains the actual ID. Hence, we shall dynamically attach the actual ID to the breadcrumb by taking the last route part and checking if it starts with :. If so, it is a dynamic route, then we get the actual ID from route.snapshot.params with its parameter name paramName.

const lastRoutePart = path.split("/").pop(); const isDynamicRoute = lastRoutePart.startsWith(":"); if (isDynamicRoute && !!route.snapshot) { const paramName = lastRoutePart.split(":")[1]; path = path.replace(lastRoutePart, route.snapshot.params[paramName]); label = route.snapshot.params[paramName]; }
  1. Generate Next URL

In every recursive loop of route, the path is fragment and a complete path is not available, such as issue-log instead of dashboard/it-helpdesk/issue-log. Therefore, a complete path needs to be re-build and attach to the breadcrumb in the current level.

const nextUrl = path ? `${url}/${path}` : url; const breadcrumb: IBreadCrumb = { label: label, url: nextUrl };
  1. Add Route with Non-empty Label and Recursive Calls

In your application, there may be some routes which does not have breadcrumb set and these routes should be ignored by the builder.

Next, if the current route has children, that means that this route is not the leaf route yet and we need to continue to make a recursive call the build next-level route.

const newBreadcrumbs = breadcrumb.label ? [...breadcrumbs, breadcrumb] : [...breadcrumbs]; if (route.firstChild) { //If we are not on our current path yet, //there will be more children to look after, to build our breadcumb return this.buildBreadCrumb(route.firstChild, nextUrl, newBreadcrumbs); } return newBreadcrumbs;
  1. Full Picture of buildBreadCrumb()
/** * Recursively build breadcrumb according to activated route. * @param route * @param url * @param breadcrumbs */ buildBreadCrumb(route: ActivatedRoute, url: string = '', breadcrumbs: IBreadCrumb[] = []): IBreadCrumb[] { //If no routeConfig is avalailable we are on the root path let label = route.routeConfig && route.routeConfig.data ? route.routeConfig.data.breadcrumb : ''; let path = route.routeConfig && route.routeConfig.data ? route.routeConfig.path : ''; // If the route is dynamic route such as ':id', remove it const lastRoutePart = path.split('/').pop(); const isDynamicRoute = lastRoutePart.startsWith(':'); if(isDynamicRoute && !!route.snapshot) { const paramName = lastRoutePart.split(':')[1]; path = path.replace(lastRoutePart, route.snapshot.params[paramName]); label = route.snapshot.params[paramName]; } //In the routeConfig the complete path is not available, //so we rebuild it each time const nextUrl = path ? `${url}/${path}` : url; const breadcrumb: IBreadCrumb = { label: label, url: nextUrl, }; // Only adding route with non-empty label const newBreadcrumbs = breadcrumb.label ? [ ...breadcrumbs, breadcrumb ] : [ ...breadcrumbs]; if (route.firstChild) { //If we are not on our current path yet, //there will be more children to look after, to build our breadcumb return this.buildBreadCrumb(route.firstChild, nextUrl, newBreadcrumbs); } return newBreadcrumbs; }

ngOnInit()

Finally, we need to implement ngOnInit() to trigger to start building the breadcrumbs.

Breadcrumb build should start when a router change event is detected. To detect it, we use RxJs to observe the changes.

ngOnInit() { this.router.events.pipe( filter((event: Event) => event instanceof NavigationEnd), distinctUntilChanged(), ).subscribe(() => { this.breadcrumbs = this.buildBreadCrumb(this.activatedRoute.root); }) }

The above code snippet indicates that the router events are observed with a filter on the event type to be NavigationEnd and a distinct change.

That means if the route is changing and the new value is different from the previous value, then the breadcrumb will start to build. The results of recursive function will be stored in this.breadcrumb, which will be an array as below.

[ { label: "Dashboard", url: "/dashboard" }, { label: "IT Helpdesk", url: "/dashboard/it-helpdesk" }, { label: "Issue Log", url: "/dashboard/it-helpdesk/issue-log" }, { label: "plfOR05NXxQ1", url: "/dashboard/it-helpdesk/issue-log/plfOR05NXxQ1" } ];

Conclusion

Breadcrumbs implement a rather simple algorithm, but I think what makes it confusing is its configurations. As developers, you need to know where the configurations should be done and the features Angular provide. With good understanding of Angular, you can implement some components easily as most of the tools you need have been provided by Angular.

You may refer to the full code here: GitHub

Thanks for reading~


Written by Yi Zhiyue A Software Engineer · 山不在高,有仙则灵
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