How to set image to fit width of the page using jsPDF?

You can get the width and height of PDF document like below,

var doc = new jsPDF("p", "mm", "a4");

var width = doc.internal.pageSize.getWidth();
var height = doc.internal.pageSize.getHeight();

Then you can use this width and height for your image to fit the entire PDF document.

var imgData = 'data:image/jpeg;base64,/9j/4AAQSkZJ......';

doc.addImage(imgData, 'JPEG', 0, 0, width, height);

Make sure that your image has the same size (resolution) of the PDF document. Otherwise it will look distorted (stretched).

If you want convert px to mm use this link http://www.endmemo.com/sconvert/millimeterpixel.php

If you need to get width 100% of PDF file and auto height you can use getImageProperties property of html2canvas library

html2canvas(input)
      .then((canvas) => {
        const imgData = canvas.toDataURL('image/png');
        const pdf = new jsPDF({
          orientation: 'landscape',
        });
        const imgProps= pdf.getImageProperties(imgData);
        const pdfWidth = pdf.internal.pageSize.getWidth();
        const pdfHeight = (imgProps.height * pdfWidth) / imgProps.width;
        pdf.addImage(imgData, 'PNG', 0, 0, pdfWidth, pdfHeight);
        pdf.save('download.pdf');
      });