Optimizing for Mobile for Our JavaScript PDF Viewer

PSPDFKit for Web has built-in mobile support for displaying your PDFs. To get the best experience for mobile, we require the viewport meta tag as shown below. This will adjust the width and scale for the mobile device and forbid pinching or double-tapping to zoom in:

  content="width=device-width, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no"

On mobile, when focusing on an input field, the browser zooms in to fit the input field to the viewport. This also happens when using search if the minimum, maximum, and initial scale don’t get added. To avoid this, just use the meta tag above.

A common layout for a (mobile) site is with a navbar or header on the top that is set to either position: fixed or position: absolute. To improve scrolling behavior on PSPDFKit for Web, you should also set the mounting container to position: fixed or position: absolute.

Here is an example of how CSS and HTML might look like with a position: fixed header:

.header {
  position: fixed;
  width: 100%;
  height: 5vh;

#pspdfkit {
  position: fixed;
  top: 5vh;
  width: 100%;
  height: calc(100% - 5vh);

A Note on vh Units

In case you didn’t notice, in the example above, we don’t use vh to define the height of #pspdfkit. The reason for this is that on iOS Safari and Chrome 56+, height: 100vh isn’t the full viewport height.

This is due to the browser’s URL bar appearing and disappearing when scrolling up or down, and the fact that browsers don’t update the computed viewport height to avoid reflows and degradation in performances — it would be hard to get 60FPS.

As it turns out though, elements with the position set to fixed and height in percentage — for example, 100% — will always fill exactly the visible height, whether or not the URL bar is shown.

For more information, we encourage you to read the URL Bar Resizing article from Google and this article from Nicolas Hoizey.