Implement ajax to send asynchronous requests (graphic tutorial)-JS Tutorial-php.cn

Home

Web Front-end

JS Tutorial

Implement ajax to send asynchronous requests (graphic tutorial)

亚连

May 21, 2018 pm 05:18 PM

ajaxasynchronousask

This article mainly teaches you how to easily implement ajax to send asynchronous requests, which has certain reference value. Interested friends can refer to

ajax sends asynchronous requests for your reference. The specific content is as follows

First step(Get XMLHttpRequest)

Ajax actually only needs to learn one object: XMLHttpRequest. If you master it, you will master ajax!!!

1. Get XMLHttpRequest

Most browsers support: var xmlHttp=new XMLHttpRequest();
IE6.0:var xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
IE5.0 uses earlier versions of IE: var xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");

2. Write a function that creates an XMLHttpRequest object

function createXMLHttpRequest(){
     try{
     return new XMLHttpRequest();
     } catch(e){
     try{
     return new ActiveXObject(“Msxml2.XMLHTTP”);
    }catch(e){
     try{
      return new ActiveXObject(“Microsoft.XMLHTTP”);
     }catch(e){
       alert(“哥们儿,你用的是什么浏览器啊?”);
       throw e;
    }
    }
     } 
}

The second step(Open the connection with the server)

xmlHttp.open(): used to open the connection with the server, it requires Three parameters:

Request method: can be GET or POST
Requested URL: Specify the server-side resource, for example:/day23_1/AServlet
Whether the request is asynchronous: If true, it means sending asynchronously request, otherwise synchronous request

xmlHttp.open("GET","/day23_1/AServlet",true);//For example

Step Three(Send Request)

xmlHttp.send(null): If not given, some browsers may not be able to send!

Parameters: Yes Request body content! If it is a GET request, null must be given.
If it is a POST request, as follows

xmlHttp.send(“username=zhangSan&password=123”);

Four steps:

0: Initialization is not completed, just created XMLHttpRequest object, the open() method has not been called yet
1: The request has started, the open() method has been called, but the send() method has not been called yet
2: The request is sent in completion status, the send() method has been called
3: Start reading the server response
4: End reading the server response (usually we only care about the last status!!!)

Get the status of the xmlHttp object

var state = xmlHttp.readyState;//可能是0、1、2、3、4

Get the status code of the server response (200: Success 304: Status has not changed 404 500: Server error)

var status=xmlHttp.status;//例如200、404、500

Get the content of the server response

var content=xmlHttp.responseText;//得到服务器的响应的文本格式的内容(这更通用)
var content=xmlHttp.responseXML;//得到服务器的响应的xml响应的内容,它是document对象了!

So the listener should be written like this

xmlHttp.onreadystatechange = function(){

  //xmlHttp的5种状态都会调用本方法
    if(xmlHttp.readyState ==4 && xmlHttp.status == 200){

  //双重判断:判断是否为4状态,而且还要判断是否为200
      var text=xmlHttp.responseText;
     } 
};

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

Ajax implementation of saving and reading uploaded images to the background (graphic tutorial)

Struts2 and Ajax data interaction (graphic tutorial)

The solution to the problem that the Ajax request is sent successfully but does not enter the success (graphic tutorial)

The above is the detailed content of Implement ajax to send asynchronous requests (graphic tutorial). For more information, please follow other related articles on the PHP Chinese website!

Statement

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

JavaScript and the Web: Core Functionality and Use CasesApr 18, 2025 am 12:19 AM

The main uses of JavaScript in web development include client interaction, form verification and asynchronous communication. 1) Dynamic content update and user interaction through DOM operations; 2) Client verification is carried out before the user submits data to improve the user experience; 3) Refreshless communication with the server is achieved through AJAX technology.

Understanding the JavaScript Engine: Implementation DetailsApr 17, 2025 am 12:05 AM

Understanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.

Python vs. JavaScript: The Learning Curve and Ease of UseApr 16, 2025 am 12:12 AM

Python is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.

Python vs. JavaScript: Community, Libraries, and ResourcesApr 15, 2025 am 12:16 AM

Python and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.

From C/C to JavaScript: How It All WorksApr 14, 2025 am 12:05 AM

The shift from C/C to JavaScript requires adapting to dynamic typing, garbage collection and asynchronous programming. 1) C/C is a statically typed language that requires manual memory management, while JavaScript is dynamically typed and garbage collection is automatically processed. 2) C/C needs to be compiled into machine code, while JavaScript is an interpreted language. 3) JavaScript introduces concepts such as closures, prototype chains and Promise, which enhances flexibility and asynchronous programming capabilities.

JavaScript Engines: Comparing ImplementationsApr 13, 2025 am 12:05 AM

Different JavaScript engines have different effects when parsing and executing JavaScript code, because the implementation principles and optimization strategies of each engine differ. 1. Lexical analysis: convert source code into lexical unit. 2. Grammar analysis: Generate an abstract syntax tree. 3. Optimization and compilation: Generate machine code through the JIT compiler. 4. Execute: Run the machine code. V8 engine optimizes through instant compilation and hidden class, SpiderMonkey uses a type inference system, resulting in different performance performance on the same code.

Beyond the Browser: JavaScript in the Real WorldApr 12, 2025 am 12:06 AM

JavaScript's applications in the real world include server-side programming, mobile application development and Internet of Things control: 1. Server-side programming is realized through Node.js, suitable for high concurrent request processing. 2. Mobile application development is carried out through ReactNative and supports cross-platform deployment. 3. Used for IoT device control through Johnny-Five library, suitable for hardware interaction.

Building a Multi-Tenant SaaS Application with Next.js (Backend Integration)Apr 11, 2025 am 08:23 AM

I built a functional multi-tenant SaaS application (an EdTech app) with your everyday tech tool and you can do the same. First, what’s a multi-tenant SaaS application? Multi-tenant SaaS applications let you serve multiple customers from a sing

See all articles