微信小程序canvas验证码生成及使用

先看效果：

wxml:

<canvas class="v-code" bindtap="changeImg" style="width:100px; height:40px;" canvas-id="canvas"></canvas>

js:

const MCAP = require('../../utils/mcaptcha');
Page({
    data: {
        codeStr: '', //生成的验证码
        code: '', //输入的验证码
    },
    /**
     * 更换验证码
     */
    changeImg: function () {
        this.initDraw();
    },
    /**
     * 制作验证码
     */
    initDraw: function () {
        var that = this;
        var codes = that.getRanNum();
        that.setData({
            codeStr: codes //生成的验证码
        })
        let mac = new MCAP({
            el: 'canvas',
            width: 100,
            height: 40,
            code: codes
        });
    },
    /**
     * 获取随机数
     */
    getRanNum: function () {
        var chars = '0123456789';
        // var chars = 'ABCDEFGHJKMNPQRSTWXYZabcdefhijkmnprstwxyz2345678';
        var pwd = '';
        for (var i = 0; i < 4; i++) {
            if (Math.random() < 10) {
                pwd += chars.charAt(Math.random() * 10 - 1);
            }
        }
        return pwd;
    },
    
})

mcaptcha.js代码：

module.exports = class Mcaptcha {
  constructor(options) {
    this.options = options;
    this.fontSize = options.height * 3 / 4;
    this.init();
    this.refresh(this.options.code);   
  }
  init() {
    this.ctx = wx.createCanvasContext(this.options.el);
    this.ctx.setTextBaseline("middle");
    this.ctx.setFillStyle(this.randomColor(180, 240));
    this.ctx.fillRect(0, 0, this.options.width, this.options.height);
  }
  refresh(code) {
    let arr = (code + '').split('');
    if (arr.length === 0) {
      arr = ['e', 'r', 'r', 'o', 'r'];
    };
    let offsetLeft = this.options.width * 0.6 / (arr.length - 1);
    let marginLeft = this.options.width * 0.2;
    arr.forEach((item, index) => {
      this.ctx.setFillStyle(this.randomColor(0, 180));      
      let size = this.randomNum(24, this.fontSize);
      this.ctx.setFontSize(size);
      let dis = offsetLeft * index + marginLeft - size * 0.3;
      let deg = this.randomNum(-30, 30);
      this.ctx.translate(dis, this.options.height * 0.5);
      this.ctx.rotate(deg * Math.PI / 180);
      this.ctx.fillText(item, 0, 0);
      this.ctx.rotate(-deg * Math.PI / 180);
      this.ctx.translate(-dis, -this.options.height * 0.5);
    })
    this.ctx.draw();
  }
  randomNum(min, max) {
    return Math.floor(Math.random() * (max - min) + min);
  }
  randomColor(min, max) {
    let r = this.randomNum(min, max);
    let g = this.randomNum(min, max);
    let b = this.randomNum(min, max);
    return "rgb(" + r + "," + g + "," + b + ")";
  }
}