怎样开发一个验证码生成插件_JavaScript验证码插件功能与安全实现方法

function Captcha(options) {
  const defaults = {
    container: null,
    width: 120,
    height: 40,
    length: 4,
    fontSize: 24,
    fontFamilies: 'Arial, Verdana, sans-serif'
  };
  this.settings = { ...defaults, ...options };
  this.canvas = null;
  this.ctx = null;
  this.code = '';
  this.init();
}

Captcha.prototype.init = function() {
  if (!this.settings.container) return;

  this.canvas = document.createElement('canvas');
  this.canvas.width = this.settings.width;
  this.canvas.height = this.settings.height;
  this.canvas.style.cursor = 'pointer';
  this.settings.container.appendChild(this.canvas);

  this.ctx = this.canvas.getContext('2d');
  this.refresh();

  // 点击刷新
  this.canvas.addEventListener('click', () => this.refresh());
};

Captcha.prototype.generateCode = function() {
  const chars = 'ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnpqrstuvwxyz23456789';
  let code = '';
  for (let i = 0; i < this.settings.length; i++) {
    code += chars.charAt(Math.floor(Math.random() * chars.length));
  }
  this.code = code;
  return code;
};

Captcha.prototype.draw = function() {
  const ctx = this.ctx;
  ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);
  ctx.fillStyle = this.randomColor(200, 255);
  ctx.fillRect(0, 0, this.canvas.width, this.canvas.height);

  // 绘制字符
  const code = this.generateCode();
  ctx.font = `${this.settings.fontSize}px ${this.settings.fontFamilies}`;
  for (let i = 0; i < code.length; i++) {
    const x = (this.canvas.width / this.settings.length) * i + 10;
    const y = this.canvas.height - 10;
    ctx.fillStyle = this.randomColor(0, 100);
    ctx.save();
    ctx.translate(x, y);
    ctx.rotate(this.randomRange(-0.5, 0.5));
    ctx.fillText(code[i], 0, 0);
    ctx.restore();
  }

  // 添加干扰线
  for (let i = 0; i < 4; i++) {
    ctx.strokeStyle = this.randomColor(180, 230);
    ctx.beginPath();
    ctx.moveTo(this.randomRange(0, this.canvas.width), this.randomRange(0, this.canvas.height));
    ctx.lineTo(this.randomRange(0, this.canvas.width), this.randomRange(0, this.canvas.height));
    ctx.stroke();
  }

  // 添加噪点
  for (let i = 0; i < 50; i++) {
    ctx.fillStyle = this.randomColor(150, 200);
    ctx.beginPath();
    ctx.arc(this.randomRange(0, this.canvas.width), this.randomRange(0, this.canvas.height), 1, 0, Math.PI * 2);
    ctx.fill();
  }
};

Captcha.prototype.randomColor = function(min, max) {
  const r = this.randomRange(min, max);
  const g = this.randomRange(min, max);
  const b = this.randomRange(min, max);
  return `rgb(${r},${g},${b})`;
};

Captcha.prototype.randomRange = function(min, max) {
  return Math.floor(Math.random() * (max - min) + min);
};

Captcha.prototype.refresh = function() {
  this.draw();
};

Captcha.prototype.getCode = function() {
  return this.code;
};

<div id="captcha-container"></div>
<script>
  const captcha = new Captcha({
    container: document.getElementById('captcha-container'),
    length: 4
  });

  // 获取当前验证码（仅用于演示，生产环境不应暴露）
  console.log(captcha.getCode()); 
</script>