url-Encode vs Base64 encoding ( usages)?

base64 is used to transfer binary data. (not supported in IE, cant encode spacial chars.)

encodeURIComponent only encodes special characters.

An interesting thing is that you can't apply base64 to unicode strings without encodeURIComponent:https://developer.mozilla.org/en/DOM/window.btoa

The answer to this is entirely dependent on your server-side application.

'+' is not translated to 'space' by the client - it is auto-translated to 'space' by some server-side apps, largely for backward-compatibility reasons (conversely, some server-side apps will leave '+' as '+' in compliance with RFC3986 ).

As far as the client is concerned - btoa() and encodeURIComponent() (and encodeURI() and escape()) just encode a string of text into different abstracted strings according to different encoding or escaping algorithms - btoa() usually produces the smallest resultant string using base64 encoding but meze's comment re: unicode is worth taking into account here.

The important thing to note is what your server-side application (some ASP.NET-based setup in your case) then uses to decode that string back to it's original form.

fwiw, I use base64 whenever I want to transport anything that CAN be unicode, between a server and a client. urlencode doesn't handle all unicode charachters all that well. It quickly gets a mess with all the percentage signs.

so, in short: expecting unicode input/output, always base64 the transportation.