Promise is the most important and difficult technology in ES6. Interviews with medium and large companies will ask about the implementation of front-end Promise. This video tutorial starts from the most basic callback/exception syntax, to the basic use of Promise; from technical analysis of Promise difficulties, to step-by-step handwritten Promise implementation, extended async and await in-depth analysis, macro queue and micro queue detailed explanation; and finally through Classic interview questions to test the effect of Promise learning. After passing the level, you will become a Promise senior engineer.