JOB Queue

MicroTask queue

In ES6 Promises were introduced as part of the native JavaScript, it is not part of WEB API. Callback Queue (Task Queue) is used to handle Web API actions, so they introduced Job Queue to handle Promises. It is same as the Callback Queue but it is smaller and higher priority than Callback Queue. So Event loop is going to look for Job Queue before looking to Callback Queue.

JavaScript Runtime after ES6 implementation