创建验证码

小知识，大挑战！本文正在参与“程序员必备小知识”创作活动

验证码干吗用？

验证码（CAPTCHA）是“Completely Automated Public Turing test to tell Computers and Humans Apart”（全自动区分计算机和人类的图灵测试的缩写，是一种区分用户是计算机还是人的公共全自动程序。
可以防止：恶意破解密码、刷票、论坛灌水，有效防止某个黑客对某一个特定注册用户用特定程序暴力破解方式进行不断的登陆尝试，实际上用验证码是现在很多网站通行的方式。

生成验证码.vue 文件

<template >
  <canvas class="canvas" ref="cav" @click="Refresh"></canvas>
</template>
<script>
export default {
  name: "ver_code",
  data () {
    return {
      show_num: []
    };
  },
  mounted () {
    this.draw();
  },
  methods: {
    draw () {
      var Canvas_DOM = this.$refs.cav;
      var cav_width = Canvas_DOM.clientWidth;
      var cav_height = Canvas_DOM.clientHeight;
      var context = Canvas_DOM.getContext("2d");
      Canvas_DOM.width = cav_width;
      Canvas_DOM.height = cav_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";
        "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
        this.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 = this._randomColor();
        context.fillText(txt, 0, 0);

        context.rotate(-deg);
        context.translate(-x, -y);
      }
      for (var i = 0; i <= 5; i++) {
        //验证码上显示随机线条
        context.strokeStyle = this._randomColor();
        context.beginPath();
        context.moveTo(
          Math.random() * Canvas_DOM.width,
          Math.random() * Canvas_DOM.height
        );
        context.lineTo(
          Math.random() * Canvas_DOM.width,
          Math.random() * Canvas_DOM.height
        );
        context.stroke();
      }
      for (var i = 0; i <= 30; i++) {
        //验证码上显示随机小点
        context.strokeStyle = this._randomColor();
        context.beginPath();
        var x = Math.random() * Canvas_DOM.width;
        var y = Math.random() * Canvas_DOM.height;
        context.moveTo(x, y);
        context.lineTo(x + 1, y + 1);
        context.stroke();
      }
    },
    _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 + ")";
    },
    Refresh () {
      this.draw();
      this.$emit("refresh_yzm", this.show_num);
    }
  }
};
</script>
<style lang="less" scoped>
.canvas {
  width: 100px;
  height: 40px;
  display: inline-block;
  margin-left: 12px;
  cursor: pointer;
}
</style>