Javascript string-replace function ignoring hyphen

I have the following code:

ttt = 'hello---,,..there';
tt2 = strip(ttt);
alert(tt2);
            
function strip(str){
  return str.replace(/[^a-zA-Z0-9 ,.-_]/g, '');
}

The alert gives hello,,..there

I would expect it to give hello---,,..there as all the characters, including hyphens, are specified as exceptions in the replacement function.

What am I doing wrong?

Answer

Escape the hyphen:

'hello---,,..there'.replace(/[^a-zA-Z0-9 ,.-_]/g, ''); // => "hello---,,..there"