echart 导出保存图片

var img = new Image();
    img.src = myChart.getDataURL({
    type:"png",
    pixelRatio: 2,
    backgroundColor: '#fff'
});

downloadWeibo(img,"微博平台-事件传播脉络",myChart.getWidth(),myChart.getHeight());

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var  downloadWeibo=function(img,name,width,height){
    console.log(img)

    img.onload=function(){
        var canvas=document.createElement("canvas");
        console.log($(img).width());
        console.log($(img).height());
        canvas.width=width*2;
        canvas.height=height*2;
        var ctx=canvas.getContext('2d');
        ctx.drawImage(img,0,0);
        canvas.toBlob(function(blob) {
            saveAs(
                blob
                , name+".png"
            );
        }, "image/png");
    }

}