I found myself in the position of building a lightweight i18n mechanism for the frontend of an enterprise app recently. I implemented a couple of decorators that inject translations into properties. I also extended the Gulp build process to gather all translation keys into a single file for me, which I could then use on the backend to deliver only the required translations, rather than send over the entire dictionary. Here’s how.

The goal is to be able to decorate a property and have access to a translation from JavaScript (injecting translations into templates is another story). It would look like this:

import { translation } from " my-translation-service " ; class MyFancyEditor { @ translation ( " editor-error-toolong " ) private errorMessageTooLong : string ; // ... validate () { if ( this . content . length > 140 ) { this . errors . push ( this . errorMessageTooLong ); } } }

I started off with stubbing the decorator:

export function translation ( textkey : string ) { return ( target : any , property : string ) => void }

Later on I also added another decorator: @translationPromise . The idea was that while @translation injects the translation once it’s loaded and doesn’t touch the property before then, the @translationPromise injects a Promise for the translation immediately, so you can wait for it if need be.

Then I went into the Gulp build progress. Typescript was compiled with gulp-typescript, based on the Aurelia skeleton project.

I used the TypeScript compiler to walk the source code Abstract Syntax Tree, looking for my new decorators and extracting the text keys used. I put this in a through-stream and plugged it into the Gulp build (line 28):

Now, whenever my TypeScript was compiled, the translation keys would be written to ../build/META-INF/frontend-textkeys.conf . Then I just read in this file in the backend, which for this project was Java EE:

Now I just need to implement a REST resource to serve the translations for every available language. And boom, translations are served:

{ " editor-error-toolong " : " Sorry, your message is longer than the maximum 140 characters! " , // and many more... }

Now I just create a frontend service to read this in, and I can implement the last puzzle piece: the decorators, which all this started with.

I hope you’ve found this useful. The code for hooking into the TS build can be used in other creative ways, I’m sure. The current implementation can’t work with dynamically composed text keys yet. If you find a clever solution for that, be sure to let me know!