js promise

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 is one of the COMMONJS specifications, with resolve, reject, done, fail, then and other methods, can help us control the flow of code, to avoid the multi-level nesting of functions. Now asynchronous is becoming more and more important in web development, for developers, this non-linear execution of the programming will make the developers feel difficult to control, and promise can let us better cont

is worth noting that when the deferred state is switched (called reject or resolve later), and then the callback function is bound, then the corresponding state of the callback function will be executed immediately.As an example:Deferred can also return its own subset of operations.promiseThere is only one API that binds the callback, and no stateful switching API.deferred: reject, resolve, done, fail, then, alwaysPromise: Done , fail, then, alwaysis obviously

JQuery's show and hide methods are well known and know that it can accept a callback function for execution after the animation completes. Like what: $ ('. Js-sam '). Hide (' slow ', function () {Alert (' You just hid Sam ');}); However, the JQuery 1.8 version also provides another writing style, namely promise– this Chinese translation is very difficult, now see there is a

Promise is being used more and more widely in JavaScript, especially in the JavaScript of server side, such as node. JS programming. Although promise has its own problems, it has its unique advantages in solving multiple nested callback and other problems.Promise common scenes are basically in the server side, but in fact, in the client side, it also has a useful

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

The most recent way to implement mock virtual data through node is to use the FS module of node to read and write to our local files to achieve a mock function: We can develop a JS file that specializes in encapsulating a simple file-reading function. The JS code is as follows: Let FS = require (' FS '); Let DEALFN = {/** * [write Data via promise] * @param {Str

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

: According to the environment in which this constant bind to the function to kill a This //Traditional JS object function person (nam E, age) {this.name=name; This.age=age; } person.prototype.showname=function () {alert (' I call ' +this.name '); }; Person.prototype.showage=function () {alert (' I ' +this.age+ ' years '); }; Let p=new person (' blue ', 18); P.showname (); P.showage (); -----------------------------------

I learned about async and promise a long time ago, but always smattering.Today, when writing Nodejs, found a lot of third-party libraries using callbacks, so in the actual operation will appear multiple callbacks, this is the legendary JS callback hell.As an example,There is a way to call Redis, access a hash object table, get the return value, and insert the return value into the other hash object table of

JavaScript is characterized by asynchrony, JavaScript can not 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 that can only be invoked when the result is available. This callback model is no problem for good code organization, but it can also solve many problems by switching from the original callback to promise