基于js和canvas的图片验证码

图片验证码一般都是后台生成的，显示到前台的。前台做验证码意义不大，因为可以被绕过。这里只是客户的一个奇葩需求，要前台实现。就借助canvas，随机生成图片实现了下，效果如下：


点击图片可以切换验证码，在输入框输入验证码，点击“验证验证码”可以判断输入的验证码是否正确，验证码不区分大小写，当然您也可以区分，改下js代码即可。验证码效果是字母+数字+不规则线条背景增加识别难度。
css代码：

.verificationCodeWrap{width: 300px; margin:50px auto;}
/*验证码*/
.verificationCode{
    width: 64px;
    height: 100%;
    margin:10px 0;
}
canvas{
    width: 100%;
    height: 100%;
}
#code_img {
    width: 100%;
    cursor: pointer;
    vertical-align: top;
}

html代码：

<div class="verificationCodeWrap">
    <label>验证码</label>
    <input type="text" id="verifital_input" class="mui-input" placeholder="请输入验证码">
    <div id="verificationCode" class="verificationCode">
        <canvas width="100" height="40" id="verifyCanvas"></canvas>
        <img id="code_img">
    </div>
    <button id="yanzheng">验证验证码</button>
</div>

js代码：

var nums = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "0", 
    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 
    'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'
];
var str = '';
var verVal = drawCode();
// 绘制验证码
function drawCode (str) {
    var canvas = document.getElementById("verifyCanvas"); //获取HTML端画布
    var context = canvas.getContext("2d"); //获取画布2D上下文
    context.fillStyle = "cornflowerblue"; //画布填充色
    context.fillRect(0, 0, canvas.width, canvas.height); //清空画布
    context.fillStyle = "white"; //设置字体颜色
    context.font = "25px Arial"; //设置字体
    var rand = new Array();
    var x = new Array();
    var y = new Array();
    for (var i = 0; i < 4; i++) {
        rand.push(rand[i]);
        rand[i] = nums[Math.floor(Math.random() * nums.length)]
        x[i] = i * 20 + 10;
        y[i] = Math.random() * 20 + 20;
        context.fillText(rand[i], x[i], y[i]);
    }
    str = rand.join('');
    //画3条随机线
    for (var i = 0; i < 3; i++) {
        drawline(canvas, context);
    }

    // 画30个随机点
    for (var i = 0; i < 30; i++) {
        drawDot(canvas, context);
    }
    convertCanvasToImage(canvas);
    return str;
}

// 随机线
function drawline (canvas, context) {
    context.moveTo(Math.floor(Math.random() * canvas.width), Math.floor(Math.random() * canvas.height)); //随机线的起点x坐标是画布x坐标0位置，y坐标是画布高度的随机数
    context.lineTo(Math.floor(Math.random() * canvas.width), Math.floor(Math.random() * canvas.height)); //随机线的终点x坐标是画布宽度，y坐标是画布高度的随机数
    context.lineWidth = 0.5; //随机线宽
    context.strokeStyle = 'rgba(50,50,50,0.3)'; //随机线描边属性
    context.stroke(); //描边，即起点描到终点
}
// 随机点(所谓画点其实就是画1px像素的线，方法不再赘述)
function drawDot (canvas, context) {
    var px = Math.floor(Math.random() * canvas.width);
    var py = Math.floor(Math.random() * canvas.height);
    context.moveTo(px, py);
    context.lineTo(px + 1, py + 1);
    context.lineWidth = 0.2;
    context.stroke();


}
// 绘制图片
function convertCanvasToImage (canvas) {
    document.getElementById("verifyCanvas").style.display = "none";
    var image = document.getElementById("code_img");
    image.src = canvas.toDataURL("image/png");
    return image;
}

// 点击图片刷新
document.getElementById('code_img').onclick = function() {
    resetCode();
}

function resetCode () {
    var verifyCanvas = document.querySelector('#verifyCanvas');
    verifyCanvas.parentNode.removeChild(verifyCanvas);
    var codeImg  = document.querySelector('#code_img');
    var verificationCode =  document.querySelector('#verificationCode');
    var oCanvas = document.createElement('canvas');
    oCanvas.width = 100;
    oCanvas.height = 40;
    oCanvas.id = 'verifyCanvas';
    verificationCode.insertBefore(oCanvas,codeImg);
    verVal = drawCode();
}

//验证验证码
document.getElementById('yanzheng').onclick = function() {
    if(document.getElementById('verifital_input').value === verVal.toUpperCase() || document.getElementById('verifital_input').value === verVal.toLowerCase() || ocument.getElementById('verifital_input').value === verVal){
        alert('正确')
    }else{
        alert('错误');
    }
}