Remove special characters (like !, >, ?, ., # etc.,) from a string using JavaScript:

var temp = new String('This is a te!!!!st st>ring... So??? What...');
document.write(temp + '<br>');
temp =  temp.replace(/[^a-zA-Z 0-9]+/g,'');
document.write(temp + '<br>');

jsFiddle

Edit:

If you don't want to remove dot(.) from string:

temp =  temp.replace(/[^a-zA-Z 0-9.]+/g,'');

Sure is!

Running this in the Firebug console

"®ü".replace(/[®ü]/g,"replaced")

returned

"replacedreplaced"

You can also do

"®ü".replace(/[\xAE\xFC]/g,"Wohoo! ");

which returns

"Wohoo! Wohoo! "

A good hex symbol lookup page can be found at http://www.ascii.cl/htmlcodes.htm

Example

running this jQuery on this page

$(".post-text").text().replace(/®/g," ******** ")

returns

" is it possible to translate special characters like ******** , ü etc with javascript 
String replace function? Use this syntax... string.replace(/\xCC/g/,''); Where 'CC' is 
the hex character code for the char you are wanting to replace. In this example I am 
replacing with empty string ''. yes, and is as simple as can be: ' ******** '.replace('
 ******** ','anything'); Sure is! Running this in the Firebug console " ******** ü".
replace(/[ ******** ü]/g,"replaced") returned replacedreplaced "

Use following code:

url.toString().replace(/&roadmap=1/g, '');

You should use the string replace function, with a single regex. Assuming by special characters, you mean anything that's not letter, here is a solution:

const str = "abc's test#s";
console.log(str.replace(/[^a-zA-Z ]/g, ""));

var desired = stringToReplace.replace(/[^\w\s]/gi, '')

As was mentioned in the comments it's easier to do this as a whitelist - replace the characters which aren't in your safelist.

The caret (^) character is the negation of the set [...], gi say global and case-insensitive (the latter is a bit redundant but I wanted to mention it) and the safelist in this example is digits, word characters, underscores (\w) and whitespace (\s).