How to use JavaScript to implement the image verification code function?-JS Tutorial-php.cn

How to use JavaScript to implement the image verification code function?

王林

Release： 2023-10-20 11:54:16

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如何使用 JavaScript 实现图片验证码功能？

How to use JavaScript to implement the image verification code function?

With the continuous development of network technology, website security has become more and more important. In operations such as registration and login, graphical verification codes are often used to ensure normal user operations and prevent access by robots or malicious programs. Graphical verification code is a verification method that displays a randomly generated verification code image and requires the user to enter the correct verification code to complete the operation.

This article will introduce how to use JavaScript to implement the image verification code function and provide specific code examples.

Preparation work

Before we start writing code, we need to prepare the following materials:

A verification code containing various characters Picture
Server-side API, used to verify whether the verification code entered by the user is correct

HTML structure

First, we need to Add a <img> tag to the file to display the verification code and a text box for entering the verification code.

<!DOCTYPE html>
<html>
<head>
  <title>图片验证码示例</title>
</head>
<body>
  <img id="captchaImage" src="captcha.jpg" alt="验证码">
  <input type="text" id="captchaInput" placeholder="请输入验证码">
  <button id="verifyButton">验证</button>

  <script src="captcha.js"></script>
</body>
</html>

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JavaScript code

Next, let us write JavaScript code to implement the verification code generation and verification functions.

// 获取页面元素
const captchaImg = document.getElementById('captchaImage');
const captchaInput = document.getElementById('captchaInput');
const verifyButton = document.getElementById('verifyButton');

// 点击验证码图片刷新验证码
captchaImg.addEventListener('click', function() {
  refreshCaptcha();
});

// 点击验证按钮进行验证码校验
verifyButton.addEventListener('click', function() {
  verifyCaptcha();
});

// 刷新验证码
function refreshCaptcha() {
  // 使用服务器端 API 获取新的验证码图片
  // 并更新验证码图片的 src 属性
  captchaImg.src = 'new_captcha.jpg';
}

// 校验验证码
function verifyCaptcha() {
  const userInput = captchaInput.value;

  // 使用服务器端 API 验证用户输入的验证码是否正确
  fetch('/verify-captcha', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({ captcha: userInput })
  })
  .then(response => response.json())
  .then(data => {
    if (data.result === 'success') {
      alert('验证码正确');
    } else {
      alert('验证码错误');
    }
  })
  .catch(error => {
    console.error('验证码校验失败', error);
  });
}

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In the above code, we use the fetch function to send an asynchronous request, and use the API provided by the server to verify the verification code. According to the verification results returned by the server, we can pop up the corresponding prompt box.

Be sure to place <script src="captcha.js"></script> at the end of the HTML file to ensure that the JavaScript code is executed after the page has finished loading.

Server-side implementation

The server-side implementation varies depending on the language and framework. Generally, the server will provide an API interface to receive the verification code entered by the user, verify it, and return the verification result.

The following is a simple Node.js server-side sample code:

const express = require('express');
const app = express();
const bodyParser = require('body-parser');

// 解析 application/json
app.use(bodyParser.json());

// 校验验证码
app.post('/verify-captcha', (req, res) => {
  const userInput = req.body.captcha;

  // 进行验证码校验
  if (userInput === 'correct_code') {
    res.json({ result: 'success' });
  } else {
    res.json({ result: 'failure' });
  }
});

const port = 3000;
app.listen(port, () => {
  console.log(`服务器运行在 http://localhost:${port}`);
});

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The /verify-captcha path in the above code corresponds to the verification interface in the front-end code , you can modify it according to the actual situation.

Summary

This article implements a simple image verification code function through the cooperation of JavaScript and the server side, including refreshing the verification code and verifying the user input. You can modify and extend the code according to actual needs to improve the security and usability of the verification code.

Finally, it is worth noting that the verification code is only a simple verification method and cannot completely prevent access by robots and malicious programs. In practical applications, we can also combine other security strategies, such as IP restrictions, user behavior analysis, etc., to improve the security of the website.

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