// 点击下载  

  downLoadCode() {
      const image = new Image();
      image.setAttribute("crossOrigin", "anonymous");
      image.onload = () => {
        const canvas = document.createElement("canvas");
        canvas.width = image.width;
        canvas.height = image.height;
        const context = canvas.getContext("2d");
        context.drawImage(image, 0, 0, image.width, image.height);
        const url = canvas.toDataURL("image/png"); // 得到图片的base64编码数据
        const a = document.createElement("a"); // 生成一个a元素
        const event = new MouseEvent("click"); // 创建一个单击事件
        a.download = `${this.rowData.deviceName}二维码`; // 设置图片名称（todo 根据你实际项目修改）
        a.href = url; // 将生成的URL设置为a.href属性
        a.dispatchEvent(event); // 触发a的单击事件
      };
      image.src = this.codeUrl;
    }

完整代码

<template>
  <el-dialog
    :destroy-on-close="true"
    :close-on-click-modal="false"
    :title="title"
    :visible.sync="dialogVisible"
    width="600px"
    @close="dialogVisible = false"
  >
    <div
      style="
        display: flex;
        flex-direction: column;
        justify-content: center;
        align-items: center;
      "
    >
      <img :src="codeUrl" class="codeImg" alt="" />
      <div class="download" @click="downLoadCode">
        <i class="iconfont if-xiazai" /><span>点击下载二维码</span>
      </div>
    </div>
  </el-dialog>
</template>

<script>
import { getQrCode } from "@/api/infoManage/deviceManage/deviceManage";
export default {
  data() {
    return {
      codeUrl: "",
      dialogVisible: false,
      title: "",
      rowData: {}
    };
  },
  methods: {
    showDialog(data) {
      this.dialogVisible = true;
      this.title = data.title;
      this.rowData = data.data;
      this.handleCode(data.data);
    },

    handleClose() {
      this.dialogVisible = false;
      this.codeUrl = "";
    },

    /**
     * 生成二维码
     * */
    handleCode(content) {
      let data = {
        content: content.id
      };
      getQrCode(data)
        .then(res => {
          const blob = new Blob([res.data], { type: "image/png" });
          this.codeUrl = window.URL.createObjectURL(blob);
        })
        .catch(err => {
          console.log(err);
        });
    },

    /**
     * 下载二维码
     * */
    downLoadCode() {
      const image = new Image();
      image.setAttribute("crossOrigin", "anonymous");
      image.onload = () => {
        const canvas = document.createElement("canvas");
        canvas.width = image.width;
        canvas.height = image.height;
        const context = canvas.getContext("2d");
        context.drawImage(image, 0, 0, image.width, image.height);
        const url = canvas.toDataURL("image/png"); // 得到图片的base64编码数据
        const a = document.createElement("a"); // 生成一个a元素
        const event = new MouseEvent("click"); // 创建一个单击事件
        a.download = `${this.rowData.deviceName}二维码`; // 设置图片名称
        a.href = url; // 将生成的URL设置为a.href属性
        a.dispatchEvent(event); // 触发a的单击事件
      };
      image.src = this.codeUrl;
    }
  }
};
</script>

<style lang="scss" scoped>
.download {
  font-size: 14px;
  font-family: MicrosoftYaHei;
  color: #1492ff;
  margin-bottom: 48px;
  cursor: pointer;
  text-align: center;
  display: flex;
  align-items: center;
  justify-content: center;
  i {
    margin-right: 5px;
  }
}
</style>