Promise is mainly used to solve the problem of asynchronous callback. There are several better solutions than promise. In this section, let's use promise to transform it. I wrote an article before. javascript Tencent Interview Question Learning Encapsulates a Simple Asynchronous Queue

An interview question (there is a button on the page, a ul, when you click the button, add a li to the back of UL every 1 second, a total of 10, the content of li starts from 0 (0, 1, 2,.... 9).

A small example of promise:

 1 function next1(){
 2     return new Promise( function( resolve, reject ){
 3         console.log( 'next1' );
 4         resolve( 'jump to next2' );
 5     } );
 6 }
 7 
 8 function next2(){
 9     return new Promise( function( resolve, reject ){
10         console.log( 'next2' );
11         resolve( 'jump to next3' );
12     } );
13 }
14 
15 next1().then( function( res ){
16     console.log( res );
17     return next2();
18 } ).then( function( res ){
19     console.log( res );
20 } );

Improvement scheme using promise:

 1 <input type="button" value="Add to">
 2 <ul></ul>
 3 <script>
 4     var oUl = document.querySelector("ul");
 5     var oBtn = document.querySelector("input");
 6     var count = 0;
 7     var timer = null;
 8     function createDom() {
 9         var oLi = document.createElement("li");
10         oLi.innerHTML = count++;
11         oUl.appendChild(oLi);
12     }
13     var addDom = (function () {
14         return new Promise(function (resolve, reject) {
15             resolve(createDom);
16         });
17     })();
18     oBtn.onclick = function () {
19         timer = setInterval(function () {
20             if (count == 10) {
21                 clearInterval(timer);
22             } else {
23                 addDom.then(function (fn) {
24                     fn();
25                 });
26             }
27         }, 1000);
28     }
29 </script>

Next, we use promise to implement a simple todolist (message board) by combining Node.js+jade+mongodb+mongoose+express.

Project structure:

The results achieved are as follows:

public: Static resources for stored projects, such as images, css,js, etc.

routers: Separate different functional modules from different routes, such as index. JS (Home Routing), add. JS (Routing When Releasing Messages)

views: jade template directory

db.js: Database Connection Module

server.js: Start Server and Project Entry

server.js:

 1 var express = require('express');
 2 var app = express();
 3 var path = require( 'path' );
 4 var indexRouter = require( './routers/index.js' );
 5 var addRouter = require( './routers/add.js' );
 6 
 7 app.use( '/', indexRouter );
 8 app.use( '/add', addRouter );
 9 app.use( express.static( path.join( __dirname, 'public' ) ) );
10 
11 app.set('views', path.join(__dirname, 'views'));
12 app.set('view engine', 'jade');
13 
14 app.listen( 3000 );
15 console.log( 'server listening on:' + 3000 );

index.js, render the home page, take out all the message data in the database

 1 var express = require('express');
 2 var router = express.Router();
 3 var Message = require('../db');
 4 
 5 function getAllMsg(){
 6     return new Promise( function( resolve, reject ){
 7         Message.find( {}, function( err, msgList ){
 8             resolve( msgList );
 9         } );
10     } );
11 }
12 router.get('/', function (req, res) {
13     getAllMsg().then( function( data ){
14         res.render( 'index', {
15             msgList : data
16         } );
17     } );
18 });
19 module.exports = router;

add.js, Handling the Promotion Procedure for Publishing Messages

 1 var express = require( 'express' );
 2 var router = express.Router();
 3 var Message = require( '../db' );
 4 
 5 function addMsg( msgInfo ){
 6     var msgModel = new Message( msgInfo );
 7     msgModel.save(function(err,result){
 8         if( err ){
 9             console.log( err );
10         }else{
11             console.log( 'success' );
12         }
13     });
14 }
15 router.get('/', function( req, res ) {
16     addMsg( {
17         title : req.query.msg,
18         listTime : new Date()
19     } );
20     res.redirect( '/' );
21 });
22 
23 module.exports = router;

db.js: Database Connection Module

 1 var mongoose = require('mongoose');
 2 mongoose.Promise = global.Promise;
 3 var DB_URL = 'mongodb://localhost:27017/cms';
 4 
 5 var db = mongoose.createConnection(DB_URL);
 6 db.on('connected', function (err) {
 7     if (err) {
 8         console.log(err);
 9     } else {
10         console.log('db connected success');
11     }
12 });
13 var Schema = mongoose.Schema;
14 var msgSchema = new Schema({
15     title: String, //Message message
16     listTime: Date //Release time
17 });
18 var Message = db.model( 'Message', msgSchema );
19 
20 module.exports = Message;

Follow-up functions:

1, delete

2, editors

3, paging

... and so on.