username username - 4 months ago 17
Javascript Question

How can you encode a string to Base64 in JavaScript?

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

If you’re writing code that doesn’t need to support IE9 or earlier, then you can use btoa() and atob() to convert to and from base64 encoding. Otherwise, use something like the function Sunny referenced.

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: