TypeScript: substitute existing type

Question

I have a project that uses AngularJS and want to make a wrapper above the $http service. I want my request promises to have abort() method.

If I write

function request(params:ng.IRequestConfig):my.IRequestPromise {
  var promise = $http(params).then(onSuccess, onError);
  promise.abort = function () { // => here it fails with error "Property 'abort' does not exist on type 'IPromise<{}>'"
    ...
  }
  return promise;
}

it fails on the line with abort definition.

I have written an interface IRequestPromise which extends ng.IPromise by adding an abort() method. How can I make TypeScript consider promise as my.IRequestPromise but not ng.IPromise ?

Answer 1

You could cast the type ( ng.IPromise ) of promise returned to your type ( my.IRequestPromise extended from ng.IPromise ):

ie

var promise = <my.IRequestPromise<yourreturntype>>$http(params).then(onSuccess, onError);

Assuming your extension is something like this:

export interface IRequestPromise<T> extends ng.IPromise<T> {
    ...
}

Also make sure your function return type is also property typed, ie

function request(params:ng.IRequestConfig):my.IRequestPromise<anyOrSpecificTypeResolvedByPromise> {