This tutorial is out of date and no longer maintained.
Note: This is part one of a two-part series where we will learn about implementing translation in our Angular 2 application.
In part 1 we will learn how to:
pipe
that we can use to translate our words in the HTML view. Like this:<!-- should display 'hola mundo' when translate to Spanish -->
<p>{{ 'hello world' | translate }}</p>
service
that we can use to translate our words in JavaScript / Typescript. Like this:...
// should display 'hola mundo' when translated to Spanish
this.translatedText = this.translate.instant('hello world'); // this.translate is our translate service
...
...
this.translate.use('es'); // use spanish
...
This is how our UI will look:
View Simple Translate Part 1 (final) on plnkr
Here’s our file structure:
|- app/
|- app.component.html
|- app.component.ts
|- app.module.ts
|- main.ts
|- translate/
|- index.ts
|- lang-en.ts
|- lang-es.ts
|- lang-zh.ts
|- translate.pipe.ts
|- translate.service.ts
|- translation.ts
|- index.html
|- systemjs.config.js
|- tsconfig.json
translate
related files.Let’s add some translations in our lang-[name].ts
files.
export const LANG_EN_NAME = 'en';
export const LANG_EN_TRANS = {
'hello world': 'hello world',
};
export const LANG_ES_NAME = 'es';
export const LANG_ES_TRANS = {
'hello world': 'hola mundo',
};
export const LANG_ZH_NAME = 'zh';
export const LANG_ZH_TRANS = {
'hello world': '你好,世界',
};
Now let’s link all the translation files in our translation.ts
file.
import { OpaqueToken } from '@angular/core';
// import translations
import { LANG_EN_NAME, LANG_EN_TRANS } from './lang-en';
import { LANG_ES_NAME, LANG_ES_TRANS } from './lang-es';
import { LANG_ZH_NAME, LANG_ZH_TRANS } from './lang-zh';
// translation token
export const TRANSLATIONS = new OpaqueToken('translations');
// all translations
const dictionary = {
[LANG_EN_NAME]: LANG_EN_TRANS,
[LANG_ES_NAME]: LANG_ES_TRANS,
[LANG_ZH_NAME]: LANG_ZH_TRANS,
};
// providers
export const TRANSLATION_PROVIDERS = [
{ provide: TRANSLATIONS, useValue: dictionary },
];
translations
. An opaque token is an object with no application interfaces. It’s a special kind of provider lookup key for use in dependency injection. For more details, please refer to Angular official document.dictionary
variable links all our translations.TRANSLATION_PROVIDERS
notes that we use the opaque token that we defined earlier, and supply our dictionary
as value. Later we will register TRANSLATION_PROVIDERS
during bootstrap (main.ts
).Let’s create our service.
import {Injectable, Inject} from '@angular/core';
import { TRANSLATIONS } from './translations'; // import our opaque token
@Injectable()
export class TranslateService {
private _currentLang: string;
public get currentLang() {
return this._currentLang;
}
// inject our translations
constructor(@Inject(TRANSLATIONS) private _translations: any) {
}
public use(lang: string): void {
// set current language
this._currentLang = lang;
}
private translate(key: string): string {
// private perform translation
let translation = key;
if (this._translations[this.currentLang] && this._translations[this.currentLang][key]) {
return this._translations[this.currentLang][key];
}
return translation;
}
public instant(key: string) {
// call translation
return this.translate(key);
}
}
Note that we import our TRANSLATIONS
token and inject it into our constructor.
Let’s now create our translation pipe. Our pipe is simple - no logic in the pipe. We will import and call our translate
service to perform the translation.
import { Pipe, PipeTransform } from '@angular/core';
import { TranslateService } from '../translate'; // our translate service
@Pipe({
name: 'translate',
})
export class TranslatePipe implements PipeTransform {
constructor(private _translate: TranslateService) { }
transform(value: string, args: any[]): any {
if (!value) return;
return this._translate.instant(value);
}
}
Both the translation service and pipe are now done. Let’s use it in our app component!
Before we can use the translation service and pipe, we need to import it to our app module.
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent } from './app.component';
import { TRANSLATION_PROVIDERS, TranslatePipe, TranslateService } from './translate';
@NgModule({
imports: [ BrowserModule ],
declarations: [ AppComponent, TranslatePipe ], // Inject Translate Pipe here
bootstrap: [ AppComponent ],
providers: [ TRANSLATION_PROVIDERS, TranslateService ]
})
export class AppModule { }
Then, we can use them in our component.
import { Component, OnInit } from '@angular/core';
import { TranslateService } from './translate';
@Component({
moduleId: module.id,
selector: 'app-root',
templateUrl: 'app.component.html',
})
export class AppComponent implements OnInit {
public translatedText: string;
public supportedLanguages: any[];
constructor(private _translate: TranslateService) { }
ngOnInit() {
// standing data
this.supportedLangs = [
{ display: 'English', value: 'en' },
{ display: 'Español', value: 'es' },
{ display: '华语', value: 'zh' },
];
// set current langage
this.selectLang('es');
}
isCurrentLang(lang: string) {
// check if the selected lang is current lang
return lang === this._translate.currentLang;
}
selectLang(lang: string) {
// set current lang;
this._translate.use(lang);
this.refreshText();
}
refreshText() {
// refresh translation when language change
this.translatedText = this._translate.instant('hello world');
}
}
supportedLanguages
to store all supported languages.navigator.language
and set the default language accordingly.translatedText
. (We can do better. We will enhance the way we handle the refresh in part 2).Here is our HTML view.
<div class="container">
<h4>Translate: Hello World</h4>
<!-- languages -->
<div class="btn-group">
<button *ngFor="let lang of supportedLangs"
(click)="selectLang(lang.value)"
class="btn btn-default" [class.btn-primary]="isCurrentLang(lang.value)">
{{ lang.display }}
</button>
</div>
<div>
<!-- translate with pipe -->
<p>
Translate With Pipe: <strong>{{ 'hello world' | translate }}</strong>
</p>
<!-- translate with service -->
<p>
Translate with Service: <strong>{{ translatedText }}</strong>
</p>
</div>
</div>
We will export our translate modules as barrel. A barrel is a way to rollup exports from several modules into a single convenience module. The barrel itself is a module file that re-exports selected exports of other modules. Refer to Angular official documentation for details.
export * from './translate.service';
export * from './translations';
export * from './translate.pipe';
Now let’s bootstrap our application.
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { AppModule } from './app.module';
const platform = platformBrowserDynamic();
platform.bootstrapModule(AppModule);
If you are using systemjs
, and use Angular CLI for project setup, please include the translate barrel in your system-config.ts file. Like this:
// App specific barrels.
'app',
'app/translate', // include this line
'app/shared',
/** @cli-barrel */
Let’s run your application. When the application loads, Spanish language is selected, and the translation shows hola mundo as expected.
Try to select English now. You should see that the Translate with pipe value is not updated.
Angular 2 Pipe is pure by default. Angular executes a pure pipe only when it detects a pure change to the input value. In our case, the input value didn’t change, it’s still Hello world
. Therefore, the value is not updated.
Let’s make our pipe impure. Angular executes an impure pipe during every component change detection cycle. In our case, when we update the language selection, change will be triggered, and the impure pipe will update accordingly.
To make our pipe impure, open app/translate/translate.pipe.ts
and add in one line:
...
@Pipe({
name: 'translate',
pure: false // add in this line, update value when we change language
})
...
Please refer to Angular 2 Pipes documentation for details on Pipe.
Yay, we have implemented our own translation. We will cover more advanced features in part 2, coming soon:
That’s it. Happy coding.
View Simple Translate Part 1 (final) on plnkr
References:
Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases.
Join our DigitalOcean community of over a million developers for free! Get help and share knowledge in our Questions & Answers section, find tutorials and tools that will help you grow as a developer and scale your project or business, and subscribe to topics of interest.
Sign up nowThis textbox defaults to using Markdown to format your answer.
You can type !ref in this text area to quickly search our full set of tutorials, documentation & marketplace offerings and insert the link!