"Invalid canvas size" while rendering PDF to PNG using pdf.js

Question

I'm having trouble making the PDF.js library render a PDF to a PNG file.

My steps are :

1. mkdir pdf-test
2. npm init
3. npm install pdfjs-dist assert canvas
4. Copy pdf2png.js from the examples page to the working folder
5. Copy a random PDF to this folder, set path to it in pdf2png.js on line 54
6. node pdf2png.js

I'm getting the following output:

# PDF document loaded.
(node:13760) UnhandledPromiseRejectionWarning: AssertionError [ERR_ASSERTION]: Invalid canvas size
    at NodeCanvasFactory_create [as create] (D:\tests\pdf-test\pdf2png.js:23:5)
    at D:\tests\pdf-test\pdf2png.js:70:21

Surprisingly, if I clone the entire PDF.js repository and follow the instructions to build it from source, the script work fine and I get a correctly rendered PNG file.

What am I missing when installing a prebuilt version from NPM?

Answer 1

You are missing an update.

The latest pdfjs-dist npm version is v2.0.943 from Oct 27, 2018, while the latest GitHub release is v2.1.266 from Feb 16, 2019.

This latest update has this changelog: migrate to canvas 2.x api which also affected pdf2png.js file, as you can see here:

So if you used the latest pdf2png.js file from pdf.js GitHub repository, you had some kind of version mismatch between the pdfjs-dist npm package and the pdf2png.js file.