Implementation principle of JSONP
This time I will bring you the implementation principle of JSONP, what are the precautions when using JSONP, the following is a practical case, let's take a look.
The implementation principle of JSONP
I believe that many people who are engaged in front-end and back-end separation are often exposed to JSONP. However, many novices do not know how to implement JSONP and its implementation principle. , this article will introduce it to you in detail. If you are interested, take a look.
Fundamental
The basic principle is easy to explain. There are some tags in HTML pages that are not subject to cross-domain restrictions, such as img, script, link, etc. If we put the data we need in a js file, then we can break through the browser's same-origin limitation.
Create script tag
Dynamic script elements are mentioned in "High Performance JavaScript", and the author writes:
1. The file starts downloading when the element is added to the page. The key point of this technology is that whenever a download is initiated, the download and execution of the file does not block other processes on the page.
2. When using dynamic script nodes to download files, the returned code will usually be executed immediately (except for Firefox and Oprea, which will wait for all previous dynamic script nodes to complete execution.) When the script executes itself, this mechanism operates normally.
Quote1 ensures that the main thread will not be blocked when making a JSONP request. Quote 2 ensures that there will be no errors when the JSONP code is executed immediately after loading.
callback
After receiving the GET request, the server usually determines whether there is a callback parameter. If so, it needs to add a method name and parentheses outside the returned data. For example, initiate the following request:
http://www.a.com/getSomething?callback=jsonp0
Then the server will return the following content:
jsonp0({code:200,data:{}})Obviously, since this is the content contained in the dynamically loaded Script tag, then this is a piece of self-executing code, and only one function of this code is called - jsonp0.
Of course, if there is execution, it must be created first, otherwise an error will be reported. This step of creation needs to be executed before calling.
The specific implementation is as follows:
function jsonp (url, successCallback, errorCallback, completeCallback) {
// 声明对象，需要将函数声明至全局作用域
window.jsonp0 = function (data) {
successCallback(data);
if (completeCallback) completeCallback();
}
// 创建script标签，并将url后加上callback参数
var
script = document.createElement('script')
, url = url + (url.indexOf('?') == -1 ? '?' : '&') + 'callback=jsonp0'
;
script.src = url;
document.head.parentNode.insertBefore(script, document.head);
// 等到script加载完毕以后，就会自己执行
}The above basically completes the core of a jsonp method. At this time, jsonp0 is a function we have declared. If the server returns normally, the jsonp0 function will be executed, and the successCallback callback inside will also be executed.
Improve it
In actual situations, there are usually many jsonp requests being called at the same time,
So since jsonp0 can meet our needs, why do we often see the code of jsonp1, jsonp2, etc. being accumulated in sequence?
This is because many requests may be made asynchronously. When the jsonp method is executed for the first time, window.jsonp0 is function A. At this time, the js file is loaded. When js is not loaded, the jsonp method is called again. At this time, window.jsonp0 points to function B. Then after the two js are loaded, the second callback will be executed.
Therefore, we need to make a distinction in the name of the callback, and accumulation can meet the needs.
Modify the code:
var jsonpCounter = 0;
function jsonp (url, successCallback, errorCallback, completeCallback) {
var jsId = 'jsonp' + jsonpCounter++;
// 声明对象，需要将函数声明至全局作用域
window[jsId] = function (data) {
successCallback(data);
if (completeCallback) completeCallback();
clean();
}
// 创建script标签，并将url后加上callback参数
var
script = document.createElement('script')
, url = url + (url.indexOf('?') == -1 ? '?' : '&') + 'callback=' + jsId
;
script.src = url;
document.head.parentNode.insertBefore(script, document.head);
// 等到script加载完毕以后，就会自己执行
//在执行完我们这个方法以后，会有很多script标签出现在head之前，我们需要手动的删除掉他们。
function clean () {
script.parentNode.removeChild(script);
window[jsId] = function(){};
}
}After adding accumulation and cleanup, there is another important point that needs to be dealt with, which is the error callback. Normally, when we request jsonp, we will set a timeout. If this time is exceeded, a timeout exception will be thrown.
The implementation is as follows:
var jsonpCounter = 0;
function jsonp (url, successCallback, errorCallback, completeCallback, timeout) {
// 略去上面写过的代码
var
timeout = timeout || 10000
, timer
;
if (timeout) {
timer = setTimeout(function () {
if (errorCallback) {
errorCallback(new Error('timeout'));
}
clean();
}, timeout)
}
function clean () {
script.parentNode.removeChild(script);
window[jsId] = function(){};
if (timer) clearTimeout(timer);
}
}In this way, all the functions of jsonp are basically completed, and the rest may require some compatible modifications to be considered a complete jsonp method.
REFER
I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!
Recommended reading:
How to pass parameters between vue-router components
Vue.js mobile component library Instructions
The above is the detailed content of Implementation principle of JSONP. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
How to implement dual WeChat login on Huawei mobile phones?
Mar 24, 2024 am 11:27 AM
How to implement dual WeChat login on Huawei mobile phones? With the rise of social media, WeChat has become one of the indispensable communication tools in people's daily lives. However, many people may encounter a problem: logging into multiple WeChat accounts at the same time on the same mobile phone. For Huawei mobile phone users, it is not difficult to achieve dual WeChat login. This article will introduce how to achieve dual WeChat login on Huawei mobile phones. First of all, the EMUI system that comes with Huawei mobile phones provides a very convenient function - dual application opening. Through the application dual opening function, users can simultaneously
PHP Programming Guide: Methods to Implement Fibonacci Sequence
Mar 20, 2024 pm 04:54 PM
The programming language PHP is a powerful tool for web development, capable of supporting a variety of different programming logics and algorithms. Among them, implementing the Fibonacci sequence is a common and classic programming problem. In this article, we will introduce how to use the PHP programming language to implement the Fibonacci sequence, and attach specific code examples. The Fibonacci sequence is a mathematical sequence defined as follows: the first and second elements of the sequence are 1, and starting from the third element, the value of each element is equal to the sum of the previous two elements. The first few elements of the sequence
How to implement the WeChat clone function on Huawei mobile phones
Mar 24, 2024 pm 06:03 PM
How to implement the WeChat clone function on Huawei mobile phones With the popularity of social software and people's increasing emphasis on privacy and security, the WeChat clone function has gradually become the focus of people's attention. The WeChat clone function can help users log in to multiple WeChat accounts on the same mobile phone at the same time, making it easier to manage and use. It is not difficult to implement the WeChat clone function on Huawei mobile phones. You only need to follow the following steps. Step 1: Make sure that the mobile phone system version and WeChat version meet the requirements. First, make sure that your Huawei mobile phone system version has been updated to the latest version, as well as the WeChat App.
How to implement exact division operation in Golang
Feb 20, 2024 pm 10:51 PM
Implementing exact division operations in Golang is a common need, especially in scenarios involving financial calculations or other scenarios that require high-precision calculations. Golang's built-in division operator "/" is calculated for floating point numbers, and sometimes there is a problem of precision loss. In order to solve this problem, we can use third-party libraries or custom functions to implement exact division operations. A common approach is to use the Rat type from the math/big package, which provides a representation of fractions and can be used to implement exact division operations.
Master how Golang enables game development possibilities
Mar 16, 2024 pm 12:57 PM
In today's software development field, Golang (Go language), as an efficient, concise and highly concurrency programming language, is increasingly favored by developers. Its rich standard library and efficient concurrency features make it a high-profile choice in the field of game development. This article will explore how to use Golang for game development and demonstrate its powerful possibilities through specific code examples. 1. Golang’s advantages in game development. As a statically typed language, Golang is used in building large-scale game systems.
PHP Game Requirements Implementation Guide
Mar 11, 2024 am 08:45 AM
PHP Game Requirements Implementation Guide With the popularity and development of the Internet, the web game market is becoming more and more popular. Many developers hope to use the PHP language to develop their own web games, and implementing game requirements is a key step. This article will introduce how to use PHP language to implement common game requirements and provide specific code examples. 1. Create game characters In web games, game characters are a very important element. We need to define the attributes of the game character, such as name, level, experience value, etc., and provide methods to operate these
Using PHP to implement SaaS: a comprehensive analysis
Mar 07, 2024 pm 10:18 PM
I'm really sorry that I can't provide real-time programming guidance, but I can provide you with a code example to give you a better understanding of how to use PHP to implement SaaS. The following is an article within 1,500 words, titled "Using PHP to implement SaaS: A comprehensive analysis." In today's information age, SaaS (Software as a Service) has become the mainstream way for enterprises and individuals to use software. It provides a more flexible and convenient way to access software. With SaaS, users don’t need to be on-premises
Detailed explanation of using Golang to implement data export function
Feb 28, 2024 pm 01:42 PM
Title: Detailed explanation of data export function using Golang. With the improvement of informatization, many enterprises and organizations need to export data stored in databases into different formats for data analysis, report generation and other purposes. This article will introduce how to use the Golang programming language to implement the data export function, including detailed steps to connect to the database, query data, and export data to files, and provide specific code examples. To connect to the database first, we need to use the database driver provided in Golang, such as da
