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try...catch when the status is reject in the promise returned by sleep.So what the hell is going on here? Let's see a picture.This code is just like the code, only after the async function is called and output a "main program is not called", the result is as followsWe find that the output is printed first, which seems to be different from our code, what's going on here.In general async/await is the promise
no new state changes are Made. therefore, There are only two final results for the Promise Object.the asynchronous Operation succeeds, the Promise object returns a value, and the state becomes Resolved. the asynchronous Operation failed, and the Promise object throws an error and the state becomes Rejected. 3. The generation of the
* */Callbacks Fs.readfile ('./promise-1.js ',' UTF8 ',function(Err, Content1) {Nesting onceConsole.log (' # ', Content1) fs.readfile ('./promise-1.js ',' UTF8 ',function (err, Content2) {//second nesting console.log ( ' # # ', Content2)}) }) //promises readfileasync (function (content1) {console.log ( ' # ', content1)
1 Promise OverviewThe Promise object is a specification proposed by the COMMONJS workgroup to provide a unified interface for asynchronous operations.So, what is promises?First, it is an object, that is, the use of other JavaScript objects is no different, and second, it acts as an agent (proxy), acting as an intermediary between the asynchronous operation and the callback function. It makes the asynchronou
The following small series will introduce you to the Usage Analysis of Promise in NodeJS. The editor thinks it is quite good. Now I will share it with you and give you a reference. Javascript is asynchronous and Javascript cannot wait. If you implement something that needs to be waited, you cannot stop there and wait until the result returns. On the contrary, the bottom line is to use callback: You define a function that can be called only when the re
Copyright NOTICE: This work is licensed under the Creative Commons Attribution-NonCommercial use-Share 4.0 International license agreement in the same way. Reprint please indicate source Http://blog.csdn.net/azureterniteDirectory (?) [+]The concept of promise The Promise object is used for asynchronous (asynchronous) computations: A Promise object repres
above, promise itself is an event publish/subscribe model.So the three functions above then are equivalent to the event binding function. (is the observer)When the previous task is deferred.resolve (data), corresponding to this task will trigger the Onfulfilled method.When the previous task is deferred.reject (err), the corresponding task will trigger the Onrejected method.Any one task, the onfulfilled or Onrejected method can only be triggered one,
Recently has been studying JS promise object, which has a blog written relatively easy to understand, forwarded as follows:Http://www.cnblogs.com/lvdabao/p/es6-promise-1.htmlReferring to the described above, I wrote the test example, understand the use of promise, and then wrote a FS
Tags: values from error message factory and nested read JSON messageRecently, while learning about node. js, I've heard that the callback hell results have been around for a week. So take the time to learn a little bit about promise. Although there are async/await, CO, generators and other options, but because I base poor, and time problems so decided to use good promis
background: Hybridapp, the front end uses Js-bridge method to call native interface, such as acquiring device information, taking pictures, face recognition and so on. The front end encapsulates the call library, and each time the native interface is called, two steps are required (1, mount the native callback function under window, 2, call the Invokenative function, send the request data) before transformation:With callbacks, you mu
ES6 in promise can be said to improve the asynchronous callback nesting problem, then if we write a library like promise how should we write?Let's take a look at the features of promise: 第一：Promise构造函数接受一个函数作为参数，函数里面有两个参数resolve和reject分别作为执行成功或者执行失败的函数var promise=New Proms
Jintiansheng: To learn a new thing, it is necessary to hold a hug mentality, if cling to their previous concept system, there will be a difficult feeling.. NET programmer first with node. JS is the most need to adapt to asynchronous development, all asynchronous, the general logic of the traversal of the list is asynchronous, how to ensure that the list traversal execution is complete? Promise help you get
{ //Ball on the left if(MarginLeftdistance) {MarginLeft++ }Else{ //the ball is on the rightmarginleft-- } //adjust the position of the ballBall.style.marginLeft=MarginLeft animate (ball, distance, CD)}, -) } //Control AnimationsAnimate (Ball1, -,function() {animate (Ball2, $, function() {animate (Ball3, Max, function() {animate (Ball2, Max, function() {animate (Ball
model change correctly$scope. $apply (function() {deferred.notify ('About to greet' +name+ '.'); if(Oktogreet (name)) {Deferred.resolve ('Hello,' +name+ '!'); } Else{deferred.reject ('Greeting' +name+ 'is not allowed.'); } }); }, +); returndeferred.promise; } varPromise=Asyncgreet ('Robin Hood'); Promise.then (function(greeting) {Console.info ('Success:' +greeting); }, function(reason) {Console.info ('Failed:' +reason); }, function(update) {Console.info ('Got Notification:
Here we will look at how to use q. js to implement node api promise.1. Everything starts with installNpm install q2. Standard node style api promise method1. Use Q. nfcallCompared with Q. fcall, Q. nfcall is the node's Q. fcall. The code is as follows:Copy code Var FS = require ('Fs '),Q = require ('Q '),Colors = require ('Colors '
Page Pages.foreach (function (HTML) {//parsing HTML varcourses=filterchapters (HTML) Coursesdata.push (Courses)})//Traverse Coursesdata.sort (function (A, b) {returna.numberThe results of the operation are as follows:650) this.width=650; "src=" Https://s2.51cto.com/wyfs02/M01/8F/50/wKiom1jahlPyvW7uAABnQMXU45E114.jpg "title=" 36020170315204858576.jpg "alt=" Wkiom1jahlpyvw7uaabnqmxu45e114.jpg "/>This article is from the "It Rookie" blog, make sure to keep this source http://mazongfei.blog.51cto.c
, the code organization also can be very not graceful, greatly reduces the code maintainability. The situation is more complex, if an operation to wait until the completion of more than one asynchronous Ajax request, there will be a callback function nesting situation, if you need to nest several layers, then you can only ask for more blessings. Let's take a look at the common asynchronous function below. var showmsg = function () { settimeout (function () { Alert (' Hello '); }
This article mainly introduces how to use Promise to encapsulate FileReader in javascript. If you need it, you can refer to Promise, which is a good choice for asynchronous processing. It can reduce the nested hierarchy and make the Code better read, the logic is clearer. ES6 adds it to the specification, and jQuery 3.0 also changes the implementation to move closer to the specification (3.0 published an an
CallbackThis is the most common and simplest, for example, in an AJAX network request, returns the data returned by the request completionThe callback function is to take a function as a parameter of another function, you can transfer local variables within the function, or you can do some asynchronous operation, call the callback function in the implementation of the function, implement the callback function in the function callThe way the callback function is closed can be the local variable f
Promise-javascript | MDNPromise-Liaoche's official website It is very convenient to use promise to make asynchronous operations synchronous, and I have been learning for a long time about the use of this promise when I am having a synchronous execution of an indeterminate number of asynchronous operations (at the time because of the lack of understanding and
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