At the heart of JavaScript’s asynchronous connection-handling are “promises,” which provide a new way of scheduling how your code will work with JavaScript APIs and functions.

We anticipate there will be other proposals.” Promises in JavaScript provide for asynchronous connection-handling, for scheduling of how code works with JavaScript APIs and functions.

An update to tiny "is-promise" library impacted millions of JavaScript projects.

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.