asynchronous javascript example

The JavaScript language execution environment is "single thread"Only one task can be completed at a time. If you have multiple tasks, you must queue, complete the previous task, and then perform the latter taskThe JavaScript language divides the execution pattern of a task into two types: synchronous (synchronous) and asynchronous (

clearly from Wikipedia's statement: First, the callback function is passed as an argument to a piece of executable code in another piece of code, which emphasizes that the callback function needs to be passed into other code as an argument; Second, the callback function can be either synchronous or asynchronous, depending on the consumer. If we go into the Wikipedia page, we can find some additional knowledge, such as the callback function will ap

callback.To understand the internal execution principle of a timer, there is an important concept that needs to be discussed: the timer delay (delay) cannot be guaranteed. Since all JavaScript code is executed in one thread, all asynchronous events (such as mouse clicks and timers) are executed only when they have execution opportunities. There is a lot of information to understand in this chart. If you fu

Asyncjs/seriesByHand. js Copy codeThe Code is as follows:Var fs = require ('fs ');Process. chdir ('referes'); // change the working directoryVar concatenation = ''; Fs. readdir ('.', function (err, filenames ){If (err) throw err; Function readFileAt (I ){Var filename = filenames [I];Fs. stat (filename, function (err, stats ){If (err) throw err;If (! Stats. isFile () return readFileAt (I + 1 ); Fs. readFile (filename, 'utf8', function (err, text ){If (err) throw err;Concatenation + = text;If (I +

', function (err, text ){If (err) throw err;Concatenation + = text;If (I + 1 === filenames. length ){// All files have been read and output can be displayed.Return console. log (concatenation );}ReadFileAt (I + 1 );});});}ReadFileAt (0 );}); As you can see, the asynchronous version has more code than the synchronous version. If you use the filter and forEach synchronization methods, the number of lines in the Code is about half, and reading is much ea

Asyncjs/seriesbyhand.js Copy Code code as follows: var fs = require (' FS '); Process.chdir (' recipes '); Change Working directory var concatenation = '; Fs.readdir ('. ', function (err, filenames) {if (err) throw err; function Readfileat (i) {var filename = filenames[i];Fs.stat (filename, function (err, stats) {if (err) throw err;if (! stats.isfile ()) return readfileat (i + 1); Fs.readfile (filename, ' UTF8 ', function (err, text) {if (err) throw err;concatenation + = t

Preface: I think the title is still quite long. There are many other functions. In fact, the simplification is just a function. asynchronous form submission only supports Image Upload under the big function of asynchronous form submission, simulate Ajax technology (in fact, it was a long time ago that it was used to implement compatibility with Ajax in multiple browsers. Here it is just a nostalgia for play

Objective: I see the title is very long, there are so many functions, in fact, the simplification is a function, asynchronous form submission, only in the asynchronous form submit this large function, can realize the image upload, simulation Ajax technology (in fact, this is the way to achieve a browser-compatible Ajax, here is only a nostalgic, As a technology to play, the following content needs to have a

JavaScript Asynchronous ProgrammingIn-depth understanding of JavaScript events? Scheduling of eventsJavaScript Event processor does not run before thread idleBlocking of threadsvar New The timing accuracy of//SetTimeout and SetInterval is lower than expected setTimeout (function() { varnew Date (); Console.log (' time elapsed ', End-start, '

This article mainly introduces javascript asynchronous programming. You can learn javascript asynchronous programming from the ground up. If you are interested in javascript asynchronous programming, refer I.

, which are synchronized with each other under the control of the kernel, such as a browser with at least 3 threads, a JavaScript engine thread, an interface rendering thread, a browser event-triggering thread, and, among other things, some executed threads. such as HTTP request threads, these asynchronous threads produce different asynchronous events.Interface R

asynchronous mode is not possible. When the page is already onload, then executing document.write will cause the contents of the current page to be emptied because it automatically triggers the Document.open method. In fact, Document.Write's reputation is not good, preferably less. Alternate Method:1. Although asynchronous loading cannot be document.write, it is possible to perform the action Dom (creatin

execution. If a piece of JavaScript is executed for a long time from start to end, any UI update will be blocked during execution, and the interface event processing will stop responding. In this case, asynchronous programming mode is required. The purpose is to scatter the code or enable I/O calls (such as AJAX) to run in the background, so that interface updates and event processing can run in a timely m

In Ajax applications, it is common to call XMLHttpRequest. Especially client-centered Ajax applications, all operations that require data retrieval from the server are completed through XHR asynchronous calls. Problem In Ajax applications, it is common to call XMLHttpRequest. Especially client-centered Ajax applications, all operations that require data retrieval from the server are completed through XHR asynchro