html2canvas(...).then is not a function

function Export() { alert("Hello! I am an alert box!! "); var element = document.getElementById(“page”);

//html2canvas(element, { logging:false}).then(function(canvas) {


 html2canvas(element, {
            onrendered: function (canvas) {


    var pdf = new jsPDF('p', 'mm', 'a4');//A4 paper, portrait
      var ctx = canvas.getContext('2d'),
       a4w = 190, a4h = 257,//A4 size, 210mm x 297mm, 10 mm margin on each side, display area 190x277
         imgHeight = Math.floor(a4h * canvas.width / a4w),//Convert pixel height of one page image to A4 display scale
         renderedHeight = 0;

    var logo = document.getElementById("logo");//Icon placed in header
    while(renderedHeight < canvas.height) {
      var page = document.createElement("canvas");
      page.width = canvas.width;
      page.height = Math.min(imgHeight, canvas.height - renderedHeight);//Maybe less than one page

      //Trim the specified area with getImageData and draw it into the canvas object created earlier
      page.getContext('2d').putImageData(ctx.getImageData(0, renderedHeight, canvas.width, Math.min(imgHeight, canvas.height - renderedHeight)), 0, 0);
      //Add an image to the page with a 10 mm / 20 mm margin
      pdf.addImage(page.toDataURL('image/jpeg', 1.0), 'JPEG', 10, 20, a4w, Math.min(a4h, a4w * page.height / page.width));
      //Add header logo
      pdf.addImage(logo, 'PNG', 5, 3);

      renderedHeight += imgHeight;
      if(renderedHeight < canvas.height)
          pdf.addPage();//Add an empty page if there is more to follow

      delete page;
    }

    pdf.save('content.pdf');
    }
  });
    }

https://github.com/niklasvh/html2canvas/releases/tag/v1.0.0-alpha.8 is the latest version