Decoding URL parameters with JavaScript

Yes it is true that decodeURIComponent function doesn't convert + to space. So you have to replace the + using replace function.

Ideally the below solution works.

var str_name = 'This+is+a+message+with+spaces';
decodeURIComponent((str_name + '').replace(/\+/g, '%20'));

Like it was pointed out already, decodeURI function doesn't convert + to space, but there are some things worth to realize here:

• decodeURI is meant to be used for whole URI, i.e. it doesn't decode separators like ?, &, =, +, etc.
• for decoding parameters decodeURIComponent should be used
  (worth to have a look at: What is the difference between decodeURIComponent and decodeURI? )
• string that you are trying to decode might actually contain + encoded as %2B, thus you should not replace + after the conversion since you might lost + signs that you actually want there, e.g. something?num=%2B632+905+123+4567 should become:
  something?num=+632 905 123 4567
  since you are probably going to extract the number: +632 905 123 4567

So the correct way to do this is:

var str = 'something?num=%2B632+905+123+4567';
decodeURIComponent( str.replace(/\+/g, '%20') );