<div class="code">
用户名:<input type="text" class="input-val"/>
<br />
密&nbsp;&nbsp;&nbsp;码:<input type="password" class="input-val"/>
<br />
验证码:<input type="text" value="" placeholder="请输入验证码（不区分大小写）" id="yzcode" class="input-val">
<canvas id="canvas" width="100" height="30"></canvas>
<button class="btn">提交</button>

 </div>

<script type="text/javascript" src="js/jquery-3.3.1.min.js" ></script>
<script>
 $(function(){
  var show_num = [];
  draw(show_num);
  $("#canvas").on(\'click\',function(){
   draw(show_num);
  })
  $(".btn").on(\'click\',function(){
   var val = $("#yzcode").val().toLowerCase();
   var num = show_num.join("");
   if(val==\'\'){
    alert(\'请输入验证码！\');
   }else if(val == num){
    alert(\'提交成功！\');
    $(".input-val").val(\'\');
    // draw(show_num);
   }else{
    alert(\'验证码错误！请重新输入！\');
    $(".input-val").val(\'\');
    // draw(show_num);
   }
  })
 })
 //生成并渲染出验证码图形
 function draw(show_num) {
  var canvas_width=$(\'#canvas\').width();
  var canvas_height=$(\'#canvas\').height();
  var canvas = document.getElementById("canvas");//获取到canvas的对象，演员
  var context = canvas.getContext("2d");//获取到canvas画图的环境，演员表演的舞台
  canvas.width = canvas_width;
  canvas.height = canvas_height;
  var sCode = "a,b,c,d,e,f,g,h,i,j,k,m,n,p,q,r,s,t,u,v,w,x,y,z,A,B,C,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,W,X,Y,Z,1,2,3,4,5,6,7,8,9,0";
  var aCode = sCode.split(",");
  var aLength = aCode.length;//获取到数组的长度
  for (var i = 0; i < 4; i++) { //这里的for循环可以控制验证码位数（如果想显示6位数，4改成6即可）
   var j = Math.floor(Math.random() * aLength);//获取到随机的索引值
   // var deg = Math.random() * 30 * Math.PI / 180;//产生0~30之间的随机弧度
   var deg = Math.random() - 0.5; //产生一个随机弧度
   var txt = aCode[j];//得到随机的一个内容
   show_num[i] = txt.toLowerCase();
   var x = 10 + i * 20;//文字在canvas上的x坐标
   var y = 20 + Math.random() * 8;//文字在canvas上的y坐标
   context.font = "bold 23px 微软雅黑";
   context.translate(x, y);
   context.rotate(deg);
   context.fillStyle = randomColor();
   context.fillText(txt, 0, 0);
   context.rotate(-deg);
   context.translate(-x, -y);
  }
  for (var i = 0; i <= 5; i++) { //验证码上显示线条
   context.strokeStyle = randomColor();
   context.beginPath();
   context.moveTo(Math.random() * canvas_width, Math.random() * canvas_height);
   context.lineTo(Math.random() * canvas_width, Math.random() * canvas_height);
   context.stroke();
  }
  for (var i = 0; i <= 30; i++) { //验证码上显示小点
   context.strokeStyle = randomColor();
   context.beginPath();
   var x = Math.random() * canvas_width;
   var y = Math.random() * canvas_height;
   context.moveTo(x, y);
   context.lineTo(x + 1, y + 1);
   context.stroke();
  }
 }
 //得到随机的颜色值
 function randomColor() {
  var r = Math.floor(Math.random() * 256);
  var g = Math.floor(Math.random() * 256);
  var b = Math.floor(Math.random() * 256);
  return "rgb(" + r + "," + g + "," + b + ")";
 }
</script>

<div class="drag">
  <div class="bg"></div>
  <div class="text" onselectstart="return false;">请拖动滑块解锁</div>
  <div class="btn">>></div>
</div>