Question

I have a PHP script that can encode a PNG image to a Base64 string.

I’d like to do the same thing using JavaScript. I know how to open files, but I’m not sure how to do the encoding. I’m not used to working with binary data.

Answer 1

You can use btoa() and atob() to convert to and from base64 encoding.

There appears to be some confusion in the comments regarding what these functions accept/return, so…

• btoa() accepts a “string” where each character represents an 8-bit byte – if you pass a string containing characters that can’t be represented in 8 bits, it will probably break. This isn’t a problem if you’re actually treating the string as a byte array, but if you’re trying to do something else then you’ll have to encode it first.

• atob() returns a “string” where each character represents an 8-bit byte – that is, its value will be between 0 and 0xff. This does not mean it’s ASCII – presumably if you’re using this function at all, you expect to be working with binary data and not text.

See also:

• How do I load binary image data using Javascript and XMLHttpRequest?

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Most comments here are outdated. You can probably use both btoa() and atob(), unless you support really outdated browsers.

Check here:

• https://caniuse.com/?search=atob
• https://caniuse.com/?search=btoa