js promise

Promise is an interface that is used to deal with objects that have such characteristics: at some point in the future (mainly asynchronous calls)is returned from the server or is populated with attributes. At its core, promise is an object with the then () function.To demonstrate its merits, take a look at an example where you need to get the user's current configuration file:1 varcurrentprofile=NULL;2 varU

Promise processes multiple interdependent asynchronous requests (for example ). In projects, multiple interdependent asynchronous requests are often encountered. If there are three ajax requests, a, B, and c, B must depend on the data returned by a, and c needs the data returned by requests a and B. If the request is nested, it is naturally not desirable. As a result, the code is difficult to maintain and many requests are requested. There will be man

Before we do that, let's take a look at Promise's call Const SRC = ' img-ph-mirror.nosdn.127.net/slp6rnbbqhy0oxfnyd9xia==/799107458981776900.jpg?imageviewthumbnail= 223x125quality=100 'Const Promise=NewPromise (function(Resovle, reject) {varimg = document.createelement (' img ')) Img.onload=function() {Resovle (img)} img.onerror=function() {Reject ()} img.src=src}) Promise.then (function(IMG) {console.log (img.width)},function() {Console.log (Error)}

Can be http://donglegend.com/2016/09/11/promise%E5%8E%9F%E7%90%86%E6%8E%A2%E7%A9%B6/to watchPromise is a what thing, we all know, degrees Niang told me, in a synchronous way to write asynchronous, solve callback hell ...State machineEarly to smell the name of promise, simple introduction, according to state changes to execute the corresponding processing function.The state of

I. Origins of Middleware A single State is stored in the store. to update a state, you must first initiate an action (through the dispatch function). Action is equivalent to a Message notification, it is used to describe what happened (for example, adding a todo), and the reducer will update the state according to the action, so that the view can be rendered based on the new state. Of course, the above is only the case of synchronous action,If action is asynchronous (for example, obtaining dat

latter maintenance up the head big AH Let's just say we can write code like this. $.getjson (apikey,{ ' uid ': Uid }). Then (function (data) {return $.getjson (apitoken,{ ' key ':d Ata.key }); }). Then (function (data) {return $.getjson (apiuserinfo,{ ' token ':d ata.token, ' uid ': Uid }) }). Then (function (user) { alert (user.name) }) Step by step down, conditioning very clear So we have to have code to support this type of writing, of c

Promise computing module monitoringThere are two parts:1. whether or not: regularly checks whether the database has new data. For example, you can obtain the max (createdate) of the promise table every 30 minutes. If this time is less than the current time by one hour, an email or SMS is triggered.Especially during the day, if there is no promise order in the las

var readinfo = function (fileName) { var defer = Q.defer (); Fs.readfile (FileName, {encoding: ' utf-8 '}, function (err, data) { if (err) { defer.reject (err) }else{ Defer.resolve (data) } ) return defer.promise;}　Readinfo (' Count.txt ') . Then (function (data) { Console.log ("Pro::", data) },function () { })　　By creating a defer object with the Promise property, call Defer.r

Promise CodeNew Promise ((Resolve) = { = = { Resolve (' Chen '); } )}); = = { console.log (value); })RXJS CodeNew OBSERVABLE (Observer) = { = setTimeout (() = { observer.next (' chen2 '); }, 4000) }) = Start.subscribe ((value) = = { console.log (value); })The difference between 1:RXJS can be canceled subscribe,

Async Version: http://blog.csdn.net/zzwwjjdj1/article/details/52129192write this version is mainly, promise more useful, and, now is the nodejs of the built-in objects, no need to reference third-party library-The tools neededMySQL DatabaseConnection database module MySQL Basic package: http://blog.csdn.net/zzwwjjdj1/article/details/51991348Auto-run module Node-schedule basic use: http://blog.csdn.net/zzwwjjdj1/article/details/51898257Generate Excel T

var getjson=function (URL) { var promise=new promise (Function (resolve,reject) { var client=new xmlhttprequest ( ); Client.open ("get", url); Client.onreadystatechange=handler; Client.responsetype= "JSON"; Client.setrequestheader ("Accept", "Application/json"); Client.send (); function handler () { if (this.readystate!==4) {return

We are looking forward to seeing our girlfriend. I met this afternoon and I don't know how to describe it. I received a short message from my girlfriend last night, saying that the two of us are over, and he does not want her to be with me in his house. Although I felt uncomfortable at the time, my body was shaking, And I calmed down after smoking a pack of cigarettes. I once promised to take good care of her, pet her, and make her happy. Maybe she is unhappy with me now. I think that since she

SourceYou can also start a chain of then() method calls via and Promise.resolve() execute the synchronous code inside a callback: function Asyncfunc () { return promise.resolve () = { Dosomethingsync (); return Dosomethingasync (); }) = {• • }); }An alternative are to start the Promise chain via the Promise constructor: function Asyncfunc

Suppose you have an application application that handles a large number of network connections, and we typically create separate processing threads for each connection. This is possible when the number of threads is small, but as the number of connections increases, a large number of threads consume a large amount of system resources. Thus, with fewer threads, it is more appropriate for each thread to handle multiple connections.STD::p romiseHere is a simple example of using

Promise is to solve the problem that the multi-layer callback function nesting structure is too deep, the code logic does not conform to the linear process. The linear process problem is solved, but the nesting structure is too deep (each layer of callback is indented more than one layer) feeling is not resolved.The traditional code for serial asynchronous loading of 3 images without extracting the function is as follows:varIMG1 =NewImage (); Img1.onl

' Use strict '; Require (' native-promise-only '); Module.exports = {wrapperrequest:function (type, URL, data, ishideloading) {var type = arguments[0], url = ARGUMENTS[1], data, ishideloading; if (arguments[2] typeof arguments[2] = = ' Boolean ') {ishideloading = arguments[2]; else {data = arguments[2]; ishideloading = arguments[3]; var loading = new Loadingservice (); if (!ishideloading) {loading.

Here we look at how to implement the node API promise with Q.js. 　　First, everything is install The code is as follows: NPM Install Q 　　Second, the standard node style API Promise method 　　1. Use Q.nfcall Relative to Q.fcall, Q.nfcall is node's q.fcall. The code is as follows: var FS = require (' FS '), Q = require (' Q '), Colors = require (' colors '), File = ' Example.txt '; var fsreadfile =

The Promise of deep learningby Yoshua BengioHumans has a long dreamed of creating machines that think. More than years before the first programmable computer is built, inventors wondered whether devices made of rods and Gears might become intelligent. And when Alan Turing, one of the pioneers of computing in the 1940s, set a goal for computer science, he described a test, Later dubbed the Turing Test, which measured a computer ' s performance against

, Access address: http://%s:%s", host, Port) }) The results are shown in chrome test. Step two: Define the hero structure (HERO.TS) Export Class Hero { Id:number; name:string; Constructor (_id:number, _name:string) { This.id = _id; THIS.name = _name; } } Step three: Writing Heroic services (hero.service.ts) Import {injectable} from ' @angular/core '; Import {Http} from "@angular/http"; Import ' Rxjs/add/operator/catch '; Import ' rxjs/

Links:JavaScript Promise: Introduction1. Chapter One chapter sequence download displayUse Array.reduce () and Promise.resolve () to concatenate the download and display of each chapter together as a whole.Download [Display] concatenation again.Promise.resolve (). [Then () and then ()]. [Then () and then ()] .... + = Series2. After each chapter has been downloaded, the chapter showsUse Array.map () to parallel the download of each chapter, using Promis