ExternalError: ReferenceError: Can't find variable: FileReader

Anvil Q&A
1

What I’m trying to do:
I have a PDF file uploader and rarely I get this error message:

Error Message: ReferenceError: Can't find variable: FileReader
        Error Status: no status
        Error Type: <class 'ExternalError'>
        JavaScript Stack Trace: @https://app.anki-buddy.com/_/static/runtime/dist/runner2.bundle.js:610:4917
Promise@[native code]
@https://app.anki-buddy.com/_/static/runtime/dist/runner2.bundle.js:1:9248
@https://app.anki-buddy.com/_/static/runtime/dist/runner2.bundle.js:610:4881
@https://app.anki-buddy.com/_/static/runtime/dist/runner2.bundle.js:610:1809
tp$descr_get@https://app.anki-buddy.com/_/static/runtime/js/lib/skulpt.min.js:551:166
$handle_pdf_upload12998$@
$PDF_uploader_change13166$@
@https://app.anki-buddy.com/_/static/runtime/js/lib/skulpt.min.js:425:408
@https://app.anki-buddy.com/_/static/runtime/dist/runner2.bundle.js:1:9847
@https://app.anki-buddy.com/_/static/runtime/js/lib/skulpt.min.js:424:498
Promise@[native code]
@https://app.anki-buddy.com/_/static/runtime/js/lib/skulpt.min.js:423:298
@https://app.anki-buddy.com/_/static/runtime/dist/runner2.bundle.js:1:9830
@https://app.anki-buddy.com/_/static/runtime/dist/runner2.bundle.js:184:2079
dispatch@https://app.anki-buddy.com/_/static/runtime/node_modules/jquery/dist/jquery.min.js:2:43095

The anvil session IDs:
N5HXHN6ISMZHUBRB4I4AGTBXO5JTWK7B
EUCG3SPSCVNZKY65DSRZ7RFF5F2MG6ZW

2

Do you know what device these users are on?

FileReader has existed in all major browsers since 2012. So having a browser that old seems unlikely. It’s possible they’re using a locked down version of a browser where FileReader isn’t available for extreme security reasons (lockdown mode on ios has this feature)

If you want program against this you could do something like

from anvil.js import window

class MyForm(MyFormTemplate):
    def __init__(self, **properties):
        if getattr(window, "FileReader", None) is None:
            alert("It looks like your browser does not support...")

Note FileReader is used by anvil to read the bytes of certain Media object

3

Any code/clone you can share?