try {
 // 将canvas对象转化为image/png
   var dataUrl = canvas.toDataURL('image/png')
 } catch (err) {
   console.log(err)
 }

<template>
    <div id="Poster">
        <div class="mask" @click="hidePoster()"></div>
        <canvas ref="canvas" width="588" height="1044" style="display:none;"></canvas>
        <div ref="box" id="Poster-box" @click.stop>
          <span class="close"  @click="hidePoster()"></span>
        </div>
        <p class="tip">长安按海报发送给朋友</p>
    </div>
</template>

<script>
export default {
  data () { // 参数
    const u = navigator.userAgent // ios终端
    const isIOS = !!u.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/) // ios终端
    return { // 返回参数
      localUrl: isIOS ? location.href.split('#')[0] : location.href, // 当前路径
      canvas: Object // canvas对象
    }
  },
  mounted () {
    this.initCanvas()
  },
  methods: {
    /**
     * 隐藏海报
     */
    hidePoster () {
      this.$emit('hide')
    },
    /**
     * 加载图片
     * @param {Object} img 图片地址
     * @return {Promise} img dom
     */
    loadImage (img) {
      return new Promise((resolve, reject) => {
        // image dom 对象
        const $image = document.createElement('img')
        if (img.isCross_domain) {
          console.log(img.url)
          $image.setAttribute('crossOrigin', 'Anonymous')
        }
        $image.onload = () => {
          resolve($image)
        }
         $image.src = img.url
        $image.onerror = reject
      })
    },
    /**
     * init初始化canvas函数
     */
    async initCanvas () {
      // 获取vue实例
      var vm = this
      vm.$indicator.open({
        text: '加载中...',
        spinnerType: 'fading-circle'
      })
      this.canvas = this.$refs.canvas.getContext('2d')
      this.canvas.height = 400
      this.canvas.width = 300
      this.canvas.fillStyle = '#ffffff'
      this.canvas.fillRect(0, 0, 588, 1044)

      // image urls
      const imgArr = [
        {
          url: require('../assets/poster-banner.png'),
          isCross_domain: false
        },
        {
          url: require('../assets/shadow.png'),
          isCross_domain: false
        },
        {
          url: 'https://s3-011-shinho-syj-uat-bjs.s3.cn-north-1.amazonaws.com.cn/mall/2019_06/border04.png',
          isCross_domain: true
        },
        {
          url: 'https://s3-011-shinho-syj-uat-bjs.s3.cn-north-1.amazonaws.com.cn/mall/2019_06/132.jpg',
          isCross_domain: true
        }
      ]
      // image doms
      await Promise.all(imgArr.map(img => this.loadImage(img))).then((imgs) => {
        console.log('done')
        this.canvas.drawImage(imgs[0], 0, 0, 588, 216 * 2)
        this.canvas.drawImage(imgs[1], 97 * 2, 166 * 2, 100 * 2, 100 * 2)

        this.canvas.save()
        this.canvas.beginPath()
        this.canvas.arc(147 * 2, 214 * 2, 34 * 2, 0, 2 * Math.PI, false)
        this.canvas.clip()
        this.canvas.drawImage(imgs[2], 113 * 2, 180 * 2, 68 * 2, 68 * 2)
        this.canvas.restore()
        this.canvas.drawImage(imgs[3], 189 * 2, 409 * 2, 88 * 2, 88 * 2)
        // 绘制文字
        this.drawText('我就是个我就账号账号', 147 * 2, 278 * 2, 290 * 2, '#333333', '32px PingFangSC-Regular ')
        this.drawText('荣誉称号是我', 147 * 2, 300 * 2, 290 * 2, '#999999', '26px PingFangSC-Regular ')
        this.drawText('距离冲榜还差10人', 147 * 2, 340 * 2, 290 * 2, '#FA6F5B', 'bold 36px arial')
        this.drawText('快来助我冲榜赢红烧酱油吧', 147 * 2, 370 * 2, 290 * 2, '#FA6F5B', 'bold 36px arial ')
        this.drawText('扫描二维码', 180 * 2, 443 * 2, 172 * 2, '#333333', '28px PingFangSC-Regular ', 'right')
        this.drawText('直达冲榜活动', 180 * 2, 463 * 2, 172 * 2, '#333333', '28px PingFangSC-Regular ', 'right')
        this.drawText('邀请好友跟你一起冲大奖', 180 * 2, 483 * 2, 172 * 2, '#333333', '28px PingFangSC-Regular ', 'right')
        this.showPic()
        vm.$indicator.close()
      })
    },
    /**
     * 绘制文字
     * @param {String} title  文字名称
     * @param {Number} x  x轴坐标
     * @param {Number} y  y轴坐标
     * @param {Number} maxwidth  最大宽度
     * @param {String} color  颜色
     * @param {String} font  字体样式
     * @param {String} textalign  文字排版
     */
    drawText (title, x, y, maxwidth, color, font, textalign = 'center') {
      this.canvas.font = font
      this.canvas.textAlign = textalign
      this.canvas.fillStyle = color
      this.canvas.fillText(title, x, y, maxwidth)
    },
    /**
     * 显示图片
     */
    showPic () {
      // 获取canvas对象
      let canvas = this.$refs.canvas

      try {
        // 将canvas对象转化为image/png
        var dataUrl = canvas.toDataURL('image/png')
      } catch (err) {
        console.log(err)
      }

      // 创建img 元素
      var newImg = document.createElement('img')
      newImg.src = dataUrl
      newImg.style.width = '100%'
      newImg.style.height = '100%'
      newImg.className = 'img-poster'
      newImg.style.borderRadius = '8px'
      this.$refs.box.appendChild(newImg)
    }

  }
}
</script>

 /**
     * 加载图片
     * @param {Object} img 图片地址
     * @return {Promise} img dom
     */
    loadImage (img) {
      return new Promise((resolve, reject) => {
        // image dom 对象
        const $image = document.createElement('img')
        $image.src = img.url
        if (img.isCross_domain) {
          console.log(img.url)
          $image.setAttribute('crossOrigin', 'Anonymous')
        }
        $image.onload = () => {
          resolve($image)
        }
        $image.onerror = reject
      })
    },

var img = new Image,
    canvas = document.createElement("canvas"),
    ctx = canvas.getContext("2d"),
    src = "http://example.com/image"; // insert image url here

img.crossOrigin = "Anonymous";

img.onload = function() {
    canvas.width = img.width;
    canvas.height = img.height;
    ctx.drawImage( img, 0, 0 );
    localStorage.setItem( "savedImageData", canvas.toDataURL("image/png") );
}
img.src = src;
// make sure the load event fires for cached images too
if ( img.complete || img.complete === undefined ) {
    img.src = "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==";
    img.src = src;
}