Create a Simple Breadcrumb in Angular
Tags: angular, typescript, javascript
Published: 2019-12-30 08:27:12

**NOTE:** This article has been archived since it was written in 2018. Now this solution may not work with the latest Angular version. You may continue reading if you would like to see the idea behind it, but may not want to follow the implementation as it is already outdated. Thanks!

Visit my Blog for the original post: [Create a Simple Breadcrumb in Angular](https://yizhiyue.me/2018/12/14/create-a-simple-breadcrumb-in-angular/)

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:**
![Imgur](https://i.imgur.com/Goczwv2.png)

**Demo for dynamic link (123 is a dynamic ID):**
![Imgur](https://i.imgur.com/SPqDKbq.png)

# 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.

```javascript
{
    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.

```javascript
{
    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`

```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`

```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`

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

### Component

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

```javascript
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.

```javascript
let label =
  route.routeConfig && route.routeConfig.data
    ? route.routeConfig.data.breadcrumb
    : "";
let path =
  route.routeConfig && route.routeConfig.data ? route.routeConfig.path : "";
```

2. Handling Dynamic Parameters
   Second, we need to handle dynamic route such as `:id`. Take a look at this route.

```javascript
{
    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`.

```javascript
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];
}
```

3. 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.

```javascript
const nextUrl = path ? `${url}/${path}` : url;

const breadcrumb: IBreadCrumb = {
  label: label,
  url: nextUrl
};
```

4. 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.

```javascript
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;
```

5. Full Picture of `buildBreadCrumb()`

```javascript
/**
 * 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.

```javascript
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.

```javascript
[
  {
    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](https://github.com/ZhiyueYi/demo-in-blog/tree/master/angular-breadcrumb-demo)**

Thanks for reading~