javascript cross-domain error

With the continuous development of front-end technology, JavaScript has become the core technology for building modern web applications. However, in practice, we often encounter JavaScript cross-domain errors. This article will introduce the causes, solutions and how to prevent JavaScript cross-domain errors from occurring.

1. Reasons for JavaScript cross-domain errors

In JavaScript, cross-domain errors refer to when a web page under one domain name initiates an HTTP request to a web page under another domain name and will be browsed. Device interception. This is because due to the same-origin policy of the browser, resources under other domain names cannot be directly accessed, that is, data sharing and interaction can only be achieved under the same domain name, port number, and protocol.

For example, when we are on a website named "www.example.com" and want to send an Ajax request to a website named "www.another-example.com", a cross-border request will occur. Domain error.

2. JavaScript cross-domain error solution

1. Use jsonp

jsonp is a way to use script tags to make cross-domain requests. In jsonp, the server wraps its response data in the callback function and then returns it to the client, and the client can obtain the data.

For example, the following code demonstrates how to use jsonp to implement cross-domain request data:

function getData() {
    var scriptElement = document.createElement('script');
    scriptElement.src = 'http://www.example.com/data?callback=handleData';
    document.querySelector('head').appendChild(scriptElement);
}

function handleData(data) {
    console.log(data);
}

2. Modify the server settings to support cross-domain requests

Configuring the CORS (Cross-Domain Resource Sharing) policy on the server side allows the client to obtain data from other domain names. For example, in Node.js, we can use the cors module to implement cross-domain requests.

const express = require('express');
const cors = require('cors');
const app = express();

app.use(cors());

app.get('/data', (req, res) => {
    res.send('data from another domain');
});

app.listen(3000, () => {
    console.log('server is running at http://localhost:3000');
});

3. Proxy server

Use a proxy server to forward cross-domain requests to the server under the target domain name, and then return the results to the client. Solve cross-domain issues.

For example, we can use nginx or Node.js as a proxy server.

3. How to prevent JavaScript cross-domain errors

Although we can use the above methods to solve cross-domain problems, in fact, the best way is to try to avoid cross-domain errors when writing code ask.

1. Use relative paths

Use relative paths to obtain resources instead of absolute paths to avoid sending requests to other domain names.

For example, in the following code, the image resource image.jpg is obtained through a relative path:

<img src="image.jpg" alt="example">

2. Using the API provided by the browser

Use the API provided by the browser to obtain resources instead of making an HTTP request to obtain resources.

For example, use the File API to get the file content instead of getting it through an Ajax request.

document.getElementById('upload').addEventListener('change', () => {
    const file = document.getElementById('upload').files[0];
    const reader = new FileReader();

    reader.onload = (e) => {
        console.log(e.target.result);
    };

    reader.readAsDataURL(file);
});

3. Use subdomain names under the same domain name

Use different subdomain names under the same domain name to provide different services respectively, so as to avoid cross-domain requests .

For example, use xxx.example.com and yyy.example.com to provide different services respectively.

Summary

JavaScript cross-domain errors are a common problem encountered in front-end development, and there are many ways to solve this problem. We can use jsonp, modify server settings and use proxy servers to solve cross-domain problems. But the best way is to try to avoid cross-domain requests when writing code, so as to better prevent cross-domain errors from occurring.

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