/**
* @ngdoc method
* @name $interval#cancel
*
* @description
* Cancels a task associated with the `promise`.
*
* @param {promise} promise A promise from calling the `$interval` function.
* @returns {boolean} Returns `true` if the task was successfully cancelled.
*/
/**
* @ngdoc service
* @name $timeout
*
* @description
* Angular's wrapper for `window.setTimeout`. The `fn` function is wrapped into a try/catch
* block and delegates any exceptions to
* {@link ng.$exceptionHandler $exceptionHandler} service.
*
* The return value of registering a timeout function is a promise, which will be resolved when
* the timeout is reached and the timeout function is executed.
*
* To cancel a timeout request, call `$timeout.cancel(promise)`.
*
* In tests you can use {@link ngMock.$timeout `$timeout.flush()`} to
* synchronously flush the queue of deferred functions.
*
* @param {function()} fn A function, whose execution should be delayed.
* @param {number=} [delay=0] Delay in milliseconds.
* @param {boolean=} [invokeApply=true] If set to `false` skips model dirty checking, otherwise
* will invoke `fn` within the {@link ng.$rootScope.Scope#$apply $apply} block.
* @returns {Promise} Promise that will be resolved when the timeout is reached. The value this
* promise will be resolved with is the return value of the `fn` function.
*
*/
首先我们看一个例子: