CODEWITHSUNDEEP
javascriptpdfpdf.js
clarkk
clarkk

Reputation: 1

pdfjs - What is a fake worker? How to solve it

I'm trying to render a PDF with PDFJS, but get a warning Setting up fake worker. What does it mean in practice?

console

Warning: Setting up fake worker.

code

<html>
    <head>
        <script src="//cdnjs.cloudflare.com/ajax/libs/pdf.js/3.0.279/pdf.min.js"></script>
        <script src="//cdnjs.cloudflare.com/ajax/libs/pdf.js/3.0.279/pdf.worker.min.js"></script>
    </head>
    <body>
        <canvas id="pdf"></canvas>
    </body>
    <script>
'use strict';

let pdfPath = 'https://path-to-pdf.pdf';
pdfjsLib.getDocument(pdfPath).promise.then(pdf=>{
    pdf.getPage(1).then(page=>{
        const viewport = page.getViewport({scale: 1}), canvas = document.getElementById('pdf'), context = canvas.getContext('2d');
        canvas.height = viewport.height;
        canvas.width = viewport.width;
        const renderContext = {
            canvasContext: context,
            viewport: viewport
        };
        page.render(renderContext);
    });
}).then(_=>{
    
}, err=>{
    console.error('Error: '+err);
});
    </script>
</html>

Upvotes: 0

Views: 5592

Answers (2)

user29786117
user29786117

Reputation: 1

The reason you're getting the fake worker and the warning is because you're importing pdf.worker.min.js in your HTML file. What you should be doing instead is setting

GlobalWorkerOptions.workerSrc = './pdf.worker.min.js'

as kca notes. But also remove the HTML script import.

Upvotes: -1

kca
kca

Reputation: 6121

The pdfjs "fake worker" behaves in the same way as the "real" worker does, but it runs in the main thread instead of a web worker.

Always use a real worker, ignoring this warning will make the website slow.

The real worker

pdfjs expects you to provide the location of the pdf.worker.js file (or pdf.worker.min.js), which comes with the pdfjs package (currently under /node_modules/pdfjs-dist/build/pdf.worker.js).

If the worker is correctly provided and its location specified, then pdfjs will create a web worker which will render PDF files "in the background", i.e. not blocking the main thread. I.e. the website stays responsive while the PDF is created.

The fake worker

If you don't set the pdf-worker, or the pdf-worker can not be found in the location that you specified, then pdfjs doesn't create a web worker, but something that looks exactly like the web worker but runs in the main thread.

As this affects the performance of the website a lot (and most often is a mistake, not intentional), pdfjs prints a warning in the console Setting up fake worker.

Solutions

Generally:

  1. The pdf worker file pdf.worker.js (or pdf.worker.min.js) must be available,
  2. pdfjs must know where the pdf worker file is

To solve the problem there are different ways, also depending on the environment and framework. Here are some hints:

  • make sure the file pdf.worker.js is reachable for your script (e.g. check by typing http://localhost:3000/pdf.worker.js in the browsers address bar). One option is to copy the file pdf.worker.js into a folder that can be reached by the browser (aka. "public folder").
  • set the workerSrc to the url of the pdf.worker.js file, like pdfjs.GlobalWorkerOptions.workerSrc = './pdf.worker.min.js'
  • make sure the version of pdfjs and pdf.worker.js are the same
  • in case of server side rendering, make sure the worker file is set in the browser, not on the server

Upvotes: 1

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