Asynchronous programming in JavaScript leverages features like callbacks, promises and async/await to sidestep this issue by allowing other code to run in the meantime.

Either of these callback functions can do any of the following: Return a new promise. In this case the result of the promise (resolving or rejecting) is delegated to this new returned promise.

Even more interesting for developers, however, is likely the upcoming addition of JavaScript Promises to IE. By default, JavaScript is single-threaded, so you can only run one script at a time.