Interface based programming with TypeScript, Angular 2 & SystemJS

Question

I\'m currently trying to clean up some code in order to program against interfaces rather than against implementations but can\'t figure out how to.

To be more speci

Answer 1

You have to keep in mind that your class may (and should) depend on abstractions, but there is one place where you can't use abstraction : it's in the dependency injection of Angular.

Angular must know what implementation to use.

Example :

/// 

module MyModule.Services {
    "use strict";

    export class LocalStorageService implements ILocalStorageService {
        public set = ( key: string, value: any ) => {
            this.$window.localStorage[key] = value;
        };

        public get = ( key: string, defaultValue: any ) => {
            return this.$window.localStorage[key] || defaultValue;
        };

        public setObject = ( key: string, value: any ) => {
            this.$window.localStorage[key] = JSON.stringify( value );
        };

        public getObject = ( key: string ) => {
            if ( this.$window.localStorage[key] ) {
                return JSON.parse( this.$window.localStorage[key] );
            } else {
                return undefined;
            }
        };

        constructor(
            private $window: ng.IWindowService // here you depend to an abstraction ...
            ) { }
    }
    app.service( "localStorageService",
        ["$window", // ... but here you have to specify the implementation
            Services.LocalStorageService] );
}

So in your test you can use mocks easily as all your controllers/services etc depend on abstractions. But for the real application, angular needs implementations.