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This article mainly introduces "Introduction and example usage of Promise object in javascript". In daily operation, I believe many people have doubts about the introduction and example usage of Promise object in javascript. Xiaobian consulted all kinds of information and sorted out simple and easy to use operation methods. I hope to answer your doubts about "Introduction and example usage of Promise object in javascript"! Next, please follow the small series to learn together!

description

A promise is an object or function with a then method.

A promise has three states: pending, rejected, and resolved.

You can only transition from pending to rejected or resolved; reject and resolved states cannot transition to each other.

A promise instance has a then method that must return a new promise.

The first callback function of the then method is called when the promise succeeds, and the second callback function is called when it fails.

examples

//asynchronous operation placed in Promise constructor const promise1 = new Promise((resolve) => { setTimeout(() => { resolve('hello'); }, 1000);});//Operation promise1.then(value => { console.log(value, 'world');}, error =>{ console.log(error, 'unhappy')}) after getting asynchronous result; At this point, the study of "Introduction and example usage of Promise object in javascript" is over, hoping to solve everyone's doubts. Theory and practice can better match to help you learn, go and try it! If you want to continue learning more relevant knowledge, please continue to pay attention to the website, Xiaobian will continue to strive to bring more practical articles for everyone!

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