Javascript - How to remove all extra spacing between words

var str = "    This    should  become   something          else   too . ";
str = str.replace(/ +(?= )/g,'');

Here's a working fiddle.

var string = "    This    should  become   something          else   too . ";
string = string.replace(/\s+/g, " ");

This code replaces a consecutive set of whitespace characters (\s+) by a single white space. Note that a white-space character also includes tab and newlines. Replace \s by a space if you only want to replace spaces.

If you also want to remove the whitespace at the beginning and end, include:

string = string.replace(/^\s+|\s+$/g, "");

This line removes all white-space characters at the beginning (^) and end ($). The g at the end of the RegExp means: global, ie match and replace all occurences.