Promise to perform multiple AJAX requests

Written in front: as an entry-level rookie, when the project cut the environment with NODE,VUE,ES6, found to learn to understand the things there are too many, before even promise is a nothing to know.

Turned over the book said promise is abstract asynchronous processing of objects and its various operations of the component, a little abstraction to understand is not AH ~ So consulted the great God

Simply put: Each asynchronous request immediately returns a Promise object, and because it returns immediately, it can take the process of synchronous operation. The promise then method allows you to specify a callback function that is called after the asynchronous task completes.

The following settimeout () can instead be interpreted as an AJAX request:

　　　　

function A () {

return new Promise (function (resolve, reject) {

SetTimeout (function () {

Console.log (' Perform task A ');

Resolve (' Perform mission a success ');

}, 1000);

});

}

Function B () {

return new Promise (function (resolve, reject) {

SetTimeout (function () {

Console.log (' Perform task B ');

Resolve (' Perform task B success ');

}, 2000);

});

}

Function C () {

Console.log (' last execution C ')

}

B is executed only after a has been successfully executed, and then C (who requests execution) after B is executed successfully

A (). Then (b ()) and then (C ());

Promise to perform multiple AJAX requests