How to export multiple pivot-grid into single pdf file

We are loading multiple pivot-grid at the same component in Angular. So, we need to export(PDF) all these grids in one pdf file. How to achieve this?
 
I have tried the following, but couldn't get it. Please reply asap.
  
exportPDF(){
var doc=newjsPDF('l', 'pt');
let docList= [];
// 'multi_pivotGrid' holds many flexmonster pivot-grid.
for (leti=0; i<multi_pivotGrid.length; i++) {
let flexmonster=multi_pivotGrid[i].flexmonster;
flexmonster.exportTo("pdf", { destinationType:"plain" }, function (res) {
var pdf=res.data;
docList.push(pdf);
doc=Object.assign({}, doc, pdf); // Didn't worked.
if (multi_pivotGrid.length==docList.length) {
doc.save("AllPivotGrids_pdf"); // Here, we need actual flexmonster 'doc'
}
else
doc.addPage();
});
}
}