Asynchronous Processing (Promises)
Promises are JavaScript objects that represent the result of an asynchronous process. After you create a promise, it acts as a placeholder for whether an operation will succeed or fail. As a promise waits in the background, the rest of your script can keep running.
In SuiteScript 2.x, all client scripts and some server scripts support promises. With promises, you can write asynchronous code that's both intuitive and efficient. SuiteScript 2.x includes promise APIs for certain modules, and you can also create custom promises in any client script.
For additional information see Promise Object.