前端pdf一次下载多个echarts图表

//需下载pdf，html2canvas 模块
savePDF:function(){
let obj1 = document.getElementById("pieChart");
let obj2 = document.getElementById("homepage-bandwidth-container");
let obj3 = document.getElementById("homepage-iops-container");
let obj4 = document.getElementById("homepage-await-container");
let arr1 = [];
arr1.push(obj1);
arr1.push(obj2);
arr1.push(obj3);
arr1.push(obj4);
let pdf = new JSPDF('', 'pt','a4');
for(let i = 0; i< arr1.length; i ++){
    html2canvas(arr1[i]).then((canvas) => {
        let pagedata = canvas.toDataURL("image/jpeg",1.0);
        let contentWidth = canvas.width;
        let contentHeight = canvas.height;
        let imgWidth = 555.28;
        let imgHeight = 555.28/contentWidth * contentHeight;
        let position = 200;
        pdf.addImage(pagedata, 'JPEG',0, position, imgWidth, imgHeight);
        if( i<arr1.length ){
            pdf.addPage(1);
        }
        
        if(i == arr1.length){
            pdf.save('图表导出'.pdf')
        }
    });
}

},