RegExp behaviour

[mailsubhra]

I have a code snippet which parses the url and returns some information after the occurrence of ? in the url:

function getValue(name) {
name = name.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");
var regexS = "[\\?&]"+name+"=([^&#]*)";
var regex = new RegExp(regexS);
var results = regex.exec(window.location.href);
if(results == null)
  return "";
else 
  return results[1];
}

If the function is called as getValue("params"); then the entire url is parsed until ?params= is found and what ever follows after that is returned.
I can also see that if the function is called as getValue("[params]"); then the line:

name = name.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");

makes name as \[params\]

Now my question is
1. What significance does [ or ] character have in JS. Why are they escaped?
2. What is being achieved by the line var regexS = "[\\?&]"+name+"=([^&#]*)";
why are we appending so many characters to name?

[Lo0kBeHiNdU]

I'll answer to yout 1st question.

"[xyz]" in RegExp is a character set, it matches any of the encolsed characters. You can spcify a range of charcters like from "A" to "Z" by using aa hyphen like this "[A-Z]".

Example: To match any of the alphabet letters you can use this.. "[A-Za-z]".

If you use it like this "[^xyz]" then it matches any of the characters that are not enclosed in this charcter set.

Hope I helped.

[mailsubhra]

Oh thanks. It did help.
How I would also like to know the significance of the [ and ] characters in
name = name.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");
how is it that if name = [params] then at the end of the above statement execution, name becomes \[params\]

[mailsubhra]

Please read "How I would also like to" as "However I would also like to"

[Declan1991]

[ is a special character, so when you want to replace [ in a string, you must use \[. Actually, that's not a great replace. This would be better.

name.replace(/\[/g,"\\\[").replace(/\]/g,"\\\]");