问题
How to add canonical link in angular 5 dynamically
<link rel="canonical" href="http://foobar.com/gotcah"/>
回答1:
Facing the same issue I searched around and found a guide on how to do this:
https://www.concretepage.com/angular/angular-title-service-and-canonical-url
It is using Angular 6 though, but I think it is backwards compatible to 5.
It basically suggests creating a Service (SEOService) for facilitating creating the canonical link whereever it is injected. It injects the Angular DOCUMENT object into the service, and creates the canonical link element as a HTMLLinkElement.
It takes care that the solution is prerendering/serverside rendering friendly - so if you are looking to better control your SEO for the pages in your application, I believe that this is what you want.
Here's a minimal rewrite of the service from the article:
seo.service.ts
import { Injectable, Inject } from '@angular/core';
import { DOCUMENT } from '@angular/common';
@Injectable({
providedIn: 'root'
})
export class SeoService {
constructor(@Inject(DOCUMENT) private doc) {}
createLinkForCanonicalURL() {
let link: HTMLLinkElement = this.doc.createElement('link');
link.setAttribute('rel', 'canonical');
this.doc.head.appendChild(link);
link.setAttribute('href', this.doc.URL);
}
}
And here's a rewrite of the component consuming the service:
data.component.ts
import { Component, OnInit } from '@angular/core';
import { SeoService } from './seo.service';
@Component({
selector: 'app-data',
templateUrl: './data.component.html'
})
export class DataComponent implements OnInit {
constructor(private seoService: SEOService) { }
ngOnInit() {
this.createLinkForCanonicalURL();
}
createLinkForCanonicalURL() {
this.seoService.createLinkForCanonicalURL();
}
}
You could simply have the createLinkForCanonicalURL() method take a optional parameter of the URL that you would want as a canonical reference for the page, for full control.
回答2:
I got the solution, create link service(ex: link.service.ts) & paste the below code :
import { Injectable, Optional, RendererFactory2, ViewEncapsulation, Inject } from '@angular/core';
import { DOCUMENT } from '@angular/platform-browser';
@Injectable()
export class LinkService {
constructor(
private rendererFactory: RendererFactory2,
@Inject(DOCUMENT) private document
) {
}
/**
* Inject the State into the bottom of the <head>
*/
addTag(tag: LinkDefinition, forceCreation?: boolean) {
try {
const renderer = this.rendererFactory.createRenderer(this.document, {
id: '-1',
encapsulation: ViewEncapsulation.None,
styles: [],
data: {}
});
const link = renderer.createElement('link');
const head = this.document.head;
const selector = this._parseSelector(tag);
if (head === null) {
throw new Error('<head> not found within DOCUMENT.');
}
Object.keys(tag).forEach((prop: string) => {
return renderer.setAttribute(link, prop, tag[prop]);
});
// [TODO]: get them to update the existing one (if it exists) ?
renderer.appendChild(head, link);
} catch (e) {
console.error('Error within linkService : ', e);
}
}
private _parseSelector(tag: LinkDefinition): string {
// Possibly re-work this
const attr: string = tag.rel ? 'rel' : 'hreflang';
return `${attr}="${tag[attr]}"`;
}
}
export declare type LinkDefinition = {
charset?: string;
crossorigin?: string;
href?: string;
hreflang?: string;
media?: string;
rel?: string;
rev?: string;
sizes?: string;
target?: string;
type?: string;
} & {
[prop: string]: string;
};
import service in component :
import { LinkService } from '../link.service';
constructor(private linkService: LinkService) {
this.linkService.addTag( { rel: 'canonical', href: 'url here'} );
}
please refer below link :
https://github.com/angular/angular/issues/15776
回答3:
If you want to add canonical link dynamically then create a simple moveToHead directive like this:
@Directive({
selector: '[appMoveToHead]'
})
export class MoveToHeadDirective implements OnDestroy, OnInit {
constructor(private renderer: Renderer2,
private elRef: ElementRef,
@Inject(DOCUMENT) private document: Document) {
}
ngOnInit(): void {
this.renderer.appendChild(this.document.head, this.elRef.nativeElement);
this.renderer.removeAttribute(this.elRef.nativeElement, 'appmovetohead');
}
ngOnDestroy(): void {
this.renderer.removeChild(this.document.head, this.elRef.nativeElement);
}
}
Here, we are removing canonical Tag from the DOM when a user navigates to another page. We do this in ngOnDestroy() of MoveToHead directive. So the case of the previous canonical tag being present in the new page is handled.
Usage: in any component.ts
canonicalLink:string;
constructor(private sanitizer: DomSanitizer) { }
//In oninit or when your data is ready, generate canonical link
ngOnInit() {
this.blogsService.getBlog(this.blogId).subscribe(data => {
let canLink = "https://example.com/blog/"+data.blogId;
// You can use pipe for sanitizing but lets do it here
this.canonicalLink = this.sanitizer.bypassSecurityTrustResourceUrl(canLink);
});
}
In any component.html template:
<div *ngIf="canonicalLink">
<link rel="canonical" appMoveToHead [attr.href]="canonicalLink" />
</div>
<div>
<!-- Other template html -->
</div>
This way you can use data bindings and all other stuff, and treat meta, link, etc., just like any other element in your template.
e.g. -
<link rel="amphtml" moveToHead [attr.href]="ampUrl">
This method works with Angular Universal (SSR) too.
Please refer below link -
https://github.com/angular/angular/issues/15776
回答4:
This applies to Angular 8 or 9, and will add canonical URLs to every page of your site.
- Create a canonical service:
// shared/canonical/canonical.service.ts
import { Injectable, Inject } from '@angular/core';
import { DOCUMENT } from '@angular/common';
@Injectable({
providedIn: 'root'
})
export class CanonicalService {
constructor(@Inject(DOCUMENT) private dom) {}
setCanonicalURL(url?: string) {
const canURL = url == undefined ? this.dom.URL : url;
const link: HTMLLinkElement = this.dom.createElement('link');
link.setAttribute('rel', 'canonical');
this.dom.head.appendChild(link);
link.setAttribute('href', canURL);
}
}
- Reference the canonical service and call it in the app component
// app.component.ts
import { CanonicalService } from './shared/services/canonical/canonical.service';
...
ngOnInit() {
this.canonicalService.setCanonicalURL();
}
...
来源：https://stackoverflow.com/questions/50737862/how-to-add-canonical-link-in-angular-5