Composing Promises
You can build promises out of other promises. In other words, you can compose promises. Composing promises is useful when you need to perform multiple asynchronous operations and wait until all or any of the operations complete.
There are two static methods of the Promise class that you can use to compose promises: the join() method and the any() method. When you join promises, a promise is complete when all of the joined promises are complete. When you use the any() method, a promise is complete when any of the promises complete.
The following code illustrates how to use the join() method. A new promise is created out of two timeout promises. The new promise does not complete until both of the timeout promises complete:
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