Why doesn't decodeURI("a+b") == "a b"?

Question

I'm trying to encode URLs in Ruby and decode them with Javascript. However, the plus character is giving me weird behavior.

In Ruby:

[Dev]> CGI.escape "a b" => "a+b" [Dev]> CGI.unescape "a+b" => "a b" 

So far so good. But what about Javascript?

>>> encodeURI("a b") "a%20b" >>> decodeURI("a+b") "a+b" 

Basically I need a method of encoding / decoding URLs that works the same way in Javascript and Ruby.

Edit: decodeURIComponent is no better:

>>> encodeURIComponent("a b") "a%20b" >>> decodeURIComponent("a+b") "a+b" 

Answer 1

+ is not considered a space. One workaround is to replace + with %20 and then call decodeURIComponent

Taken from php.js' urldecode:

decodeURIComponent((str+'').replace(/\+/g, '%20')); 

Answer 2

From MDC decodeURI:

Does not decode escape sequences that could not have been introduced by encodeURI.

From MDC encodeURI:

Note that encodeURI by itself cannot form proper HTTP GET and POST requests, such as for XMLHTTPRequests, because "&", "+", and "=" are not encoded