Shulou(Shulou.com)06/01 Report--

Most people do not understand the knowledge points of this "how to construct JavaScript Promise" article, so the editor summarizes the following content, detailed content, clear steps, and has a certain reference value. I hope you can get something after reading this article. Let's take a look at this "how to construct JavaScript Promise" article.

Promise is a class provided by ECMAScript 6 that aims to write complex asynchronous tasks more elegantly.

Because Promise is a new addition to ES6, some old browsers don't support it. Apple's Safari 10 and Windows's Edge 14 and above began to support ES6 features.

Construct Promise

Now let's create a new Promise object:

New Promise (function (resolve, reject) {

/ / what needs to be done.

})

Creating a new Promise object doesn't seem to see how it "writes complex asynchronous tasks more elegantly." The asynchronous tasks we have encountered before are all asynchronous once. What if we need to call asynchronous functions multiple times? For example, if I want to output the string three times, the first interval is 1 second, the second interval is 4 seconds, and the third interval is 3 seconds:

Case study

SetTimeout (function () {

Console.log ("First")

SetTimeout (function () {

Console.log ("Second")

SetTimeout (function () {

Console.log ("Third")

}, 3000)

}, 4000)

}, 1000)

This program implements this function, but it is implemented in a "function waterfall". It is conceivable that in a complex program, the program implemented with "function waterfall" is particularly tedious in terms of maintenance and exception handling, and will make the indentation format very redundant.

Now let's use Promise to do the same thing:

Case study

New Promise (function (resolve, reject) {

SetTimeout (function () {

Console.log ("First")

Resolve ()

}, 1000)

}) .then (function () {

Return new Promise (function (resolve, reject) {

SetTimeout (function () {

Console.log ("Second")

Resolve ()

}, 4000)

})

}) .then (function () {

SetTimeout (function () {

Console.log ("Third")

}, 3000)

})

This code is long, so you don't need to fully understand it, and what I want to notice is that Promise turns nested format code into sequential format code.

The above is the content of this article on "how to construct JavaScript Promise". I believe we all have a certain understanding. I hope the content shared by the editor will be helpful to you. If you want to know more about the relevant knowledge, please pay attention to the industry information channel.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.