javascript canvas转图片下载

1. 将canvas转为base64格式。

2. 将base64转为blob格式

downloadImg(){
        let echartsImg = $('#chart').find('canvas')[0];
        let img = echartsImg.toDataURL("image/jpeg");
        //下载
        this.downloadFile('img',img)
      },
      //base64转blob
      base64ToBlob(code) {
        let parts = code.split(';base64,');
        let contentType = parts[0].split(':')[1];
        let raw = window.atob(parts[1]);
        let rawLength = raw.length;

        let uInt8Array = new Uint8Array(rawLength);

        for (let i = 0; i < rawLength; ++i) {
          uInt8Array[i] = raw.charCodeAt(i);
        }
        return new Blob([uInt8Array], {type: contentType});
      },

      //下载
      downloadFile(fileName, content) {
        let aLink = document.createElement('a');
        let blob = this.base64ToBlob(content); //new Blob([content]);

        let evt = document.createEvent("HTMLEvents");
        evt.initEvent("click", true, true);//initEvent 不加后两个参数在FF下会报错  事件类型，是否冒泡，是否阻止浏览器的默认行为
        aLink.download = fileName;
        aLink.href = URL.createObjectURL(blob);

        aLink.dispatchEvent(new MouseEvent('click', {bubbles: true, cancelable: true, view: window}));//兼容火狐
      },