AngularJS $q Promise Delayer

In class a couple months ago (the Angular Boot Camp I often teach), a student asked how to do something like Thread.sleep(n) in JavaScript. Of course there isn’t such a thing, at least in the main JS execution environments (browsers, Node). Rather there is the asynchronous equivalent of setTimeout().

But there is an equivalent, nearly as terse way to insert a delay in a promise chain. Here is a short (thought perhaps not optimally short) sleep equivalent. This is for use in an AngularJS app, with its $q promise implementation.

angular.module("whatever", [])

.factory("kcSleep", function($timeout) {
  return function(ms) {
    return function(value) {
      return $timeout(function() {
        return value;
      }, ms);
    };
  };
});

// to use it:

somePromise
  .then(kcSleep(1000))
  .then(whatever);