<div class="layui-form-item">
    <div class="layui-col-xs6" >
      <input type="text" value="" placeholder="请输入验证码（不区分大小写）" class="input-val"> 
      <canvas id="canvas" width="100" height="30"></canvas>  
     </div>
      <div>
      <input type="button" value="登录"  class="layui-btn layui-btn-fluid" lay-submit lay-filter="login"> 
      </div>         
</div>

var show_num=[];
  $(function()
  {
   draw(show_num);
   $("#canvas").on('click',function()
   {
  draw(show_num);      
   })      
  }); 

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,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 <= 3; i++) {
                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 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();
            }
        }

        function randomColor() {//得到随机的颜色值
            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 + ")";
        }

<style>
        .code {
            width: 100%;
            margin: 0 auto;
        }
        .input-val {
            width: 63%;
            background: #ffffff;
            height: 2.8rem;
            padding: 0 2%;
            border-radius: 5px;
            border: none;
            border: 1px solid rgba(0,0,0,.2);
            font-size: 0.9rem;
        }
        #canvas {
            float: right;
            display: inline-block;
            border: 1px solid #ccc;
            border-radius: 5px;
            cursor: pointer;
        }
</style>