DOM Exception 5 INVALID CHARACTER error on valid base64 image string in javascript

I’m trying to decode a base64 string for an image back into binary so it can be downloaded and displayed locally by an OS.

The string I have successfully renders when put as the src of an HTML IMG element with the data URI preface (data: img/png;base64, ) but when using the atob function or a goog closure function it fails.

However decoding succeeds when put in here:

Any ideas?

I successfully got it to decode with another library other than the built-in JS function. But, it still won’t open locally – on a Mac says it’s damaged or in an unknown format and can’t get opened.

The code is just something like:

imgEl.src=";base64," + contentStr; //this displays successfully
decodedStr = window.atob(contentStr); //this throws the invalid char exception but i just
//used a different script to get it decode successfully but still won't display locally

the base64 string itself is too long to display here (limit is 30,000 characters)

I was just banging my head against the wall on this one for awhile.

There are a couple of possible causes to the problem. 1) Utf-8 problems. There’s a good write up + a solution for that here.

In my case, I also had to make sure all the whitespace was out of the string before passing it to atob. e.g.

function decodeFromBase64(input) {
  input = input.replace(/\s/g, '');
  return atob(input);

What was really frustrating was that the base64 parsed correctly using the base64 library in python, but not in JS.

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