node. JS encapsulates an asynchronous function with ES6 native promise

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The concept of promise

The Promise object is used for asynchronous (asynchronous) computations: A Promise object represents an operation that has not yet been completed but is expected to be completed in the future.

Several states of promise:

• Pending: The initial state, that is, the execution of the wait operation
• Fulfilled: Successful operation
• Rejected: Failed operation

The state of the pending can either be converted to fulfilled or rejected, and when the state changes, the Promise.then (onfulfilled, onrejected) method is called

Basic usage of Promise

1. First create an instance of promise

var promise = new Promise(function(resolve, reject){ //do something if(success){ resolve(value); } else { reject(value); }});

Using promise to encapsulate asynchronous functions

The IO operation in node. JS is asynchronous, so it's easy to fall into the callback pit during the writing of the async program.

Knowing the basic call procedure of promise, we can use it to encapsulate asynchronous functions.

1. Defining functions

functionSendRequest(){ReturnNew Promise (function(Resolve, Reject) { var req = http.request (options, function(res) { var data = '; Res.on (' data ', function(chunk) {data + = chunk;}); Res.on (' end ', function() { ////Successful call resolve (data);}); }); Req.on (' error ', function(err) { //] call reject (ERR) after failure;}); Req.end ();});     

2. Calling functions

sendRequest().then(function(data){    console.log(data);}).catch(function(err){ console.log(err);});

node. JS encapsulates an asynchronous function with ES6 native promise