Range out of order in character class in javascript
Solution 1:
Because you create the RegExp using a String the _\-\. becomes _-. and that is the invalid range.
(It is a range from _ to . and that is not correct)
You need to double escape it:
new RegExp("^([A-Za-z0-9_\\-\\.])+@" + domain + "$");
That way the \\ becomes a \ in the String and then is used to escape the -in the RegExp.
EDIT:
If you create RegExp by String it is always helpful to log the result so that you see if you did everything right:
e.g. your part of the RegExp
console.log("^([A-Za-z0-9_\-\.])+\@");
results in:
^([A-Za-z0-9_-.])+@