promise chaining

summarizing the use of promise in JavaScript programming Promise Core DescriptionAlthough promise has its own specifications, but the current various types of promise libraries, in the promise implementation of the details are different, and some of the API even in the sens

processed. In addition, a new component-web Worker is introduced in HTML5, which can perform these tasks outside of the JavaScript thread without blocking the current UI thread.The event loop model in the browser looks like this:Because of this internal event-looping mechanism in the browser, JavaScript always handles event tasks in a callback callback manner. So there is no avoiding the processing of multiple JavaScript asynchronous tasks, and will encounter "Callback Hell" (Callback Hell), ma

1. A preliminary understanding of promise from a macroscopic perspective Promise meaning is not the literal "oath" or "promise", but the meaning of "prophet". Although human behavior can be parallel, conscious thinking activities show a single-threaded nature. For example, ordinary people can only think of one problem at a time. In the process of thinking, it is

Describes the role of jQuery's promise object in JavaScript asynchronous programming, jquerypromise Promise, which can be understood as a desire in Chinese, represents the final result of a single operation. A Promise has three statuses: unfulfilled (not satisfied), fulfilled (satisfied), failed (failed), fulfilled status, and failed status. A desire can be chang

1.Promise IntroductionPromise is the first community proposed and implemented, the latter ES6 to write to the standard, and the original Promise object, is an asynchronous programming solution, the specific concept you can go to view the relevant information. Traditionally, handling asynchrony is done in the form of a callback callback function, but when the callback is nested too much, it makes the program

ES6 new feature 6: Detailed description of the promise object instance, es6promise This example describes the promise object of the new ES6 feature. We will share this with you for your reference. The details are as follows: 1. Introduction to promise It is an object, which is similar to other JavaScript objects. Second, it acts as a proxy ),Acts as an intermedia

Examples of Promise asynchronous programming // 1. solve the asynchronous callback problem // 1.1 how to synchronize asynchronous requests // if there are no pre-and post-order differences between several asynchronous operations, the subsequent tasks can be executed only after multiple asynchronous operations are completed, const fs = require ('fs'); let school ={}; fs. readFile ('. /name.txt ', 'utf8', function (err, data) {school. name = data;}); f

to just append the callbacks to their respective call locations in the previous way. Suitable for these asynchronous operations, you can write more elegant code is promise.Promise play . What is promise? Let's go ahead and take the AJAX request schematic code in front of jquery as an example, and that code can actually be written like this: var promise = $.ajax ({ url:url, data:dataobject });

First, promise related Https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Promise http://liubin.org/promises-book/#chapter1-what-is-promise The new Promise (/ * Executor:executor is a function with resolve and reject two parameters. * /function (resolve, reject) {...} );Change the

This article, mainly popularize the usage of promise. All along, JavaScript processing asynchronous is in the callback way, in the front-end development field callback mechanism almost popular. When designing APIs, both the browser manufacturer and the SDK developer, or the authors of various libraries, have basically followed the callback routines. In recent years, as the JavaScript development model gradually matured, COMMONJS standard homeopathy,

5 Promise.all () The Promise.all method is used to wrap multiple Promise instances into a new Promise instance.var p = promise.all ([p1, p2, p3]);In the code above, the Promise.all method accepts an array as an argument, p1, p2, and P3 are instances of the Promise object, and if not, the Promise.resolve method described below is invoked to convert the argument to

Promise, Chinese can be understood as a desire to represent the end result of a single operation. A promise has three states: unfulfilled (unsatisfied), fulfilled (satisfied), failed (failed), fulfilled state and failed state can be monitored. A wish can never be satisfied with a state of satisfaction or failure, once a desire is in a state of satisfaction or failure, its state will no longer change. This "

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

The real problem with callback functions is that they deprive us of the ability to use the return and throw keywords. Promise solves all this well. Promise in js The real problem with callback functions is that they deprive us of the ability to use the return and throw keywords. Promise solves all this well. In June 2015, the official version of ECMAScript 6 w

In the process of writing node.js, continuous IO operations can lead to "pyramid Nightmare", the callback function of multiple nesting makes the code difficult to maintain, using COMMONJS promise to encapsulate asynchronous functions, using a unified chain API to escape the nightmare of multiple callbacks. The non-blocking IO model provided by Node.js allows us to handle IO operations in the form of callback functions, however, when continuous IO ope

I. PromiseJS Animation settimeout,setinterval,requestanimationframe,promiseNPM Install BluebirdJavaScript is characterized by async, JavaScript can't wait, if you implement something that needs to wait, you can't stop there waiting for the result to come back, instead, the bottom line is to use the callback callback: You define a function,　This function cannot be called until the result is available. This callback model is not a problem for good code organization, but it can also solve many prob

First, the preface In order to get the front end back to heaven from the hell of the callback, JQuery also introduced the concept of Promise. Promise is an abstraction that makes code asynchronous behavior more elegant, and with it we can write asynchronous code like write synchronization code. JQuery began with the 1.5 version of the COMMONJS promise/a specific