Returning an AngularJS $q promise with TypeScript

Question

I have a service that wraps $http with my functions returning a deferred object.

My interface:

export interface MyServiceScope {
    get: ng.IPromise<{}>;
}

My class:

export class MyService implements MyServiceScope {

    static $inject = ['$http', '$log'];

    constructor(private $http: ng.IHttpService,
                private $log: ng.ILogService,
                private $q: ng.IQService) {
        this.$http = $http;
        this.$log = $log;
        this.$q = $q;
    }

    get(): ng.IPromise<{}> {
        var self = this;
        var deferred = this.$q.defer();

        this.$http.get('http://localhost:8000/tags').then(
            function(response) {
                deferred.resolve(response.data);
            },
            function(errors) {
                self.$log.debug(errors);
                deferred.reject(errors.data);
            }
        );

        return deferred.promise;
    }
}

The compilation is failing with the following error:

myservice.ts(10,18): error TS2420: Class 'MyService' incorrectly implements interface 'MyServiceScope'.
    Types of property 'get' are incompatible.
        Type '() => IPromise<{}>' is not assignable to type 'IPromise<{}>'.
            Property 'then' is missing in type '() => IPromise<{}>'.

For reference, here is the IPromise definition from DefinitelyTyped. The IQService.defer() call returns an IDeferred object, and then deferred.promise returns IPromise object.

I'm not sure if I'm using the wrong definitions in my interface, or not returning the deferred object the same way. Any input would be greatly appreciated!

Answer 1

In your interface you defined a property get and in the service implementation it's a function get(). What you probably want is a function, so the interface should be:

export interface MyServiceScope {
    get(): ng.IPromise<{}>;
}