using javascript new regexp object for brackets containing set of matching characters

Question

So looks like I have ran into a weird problem and was wondering whether somebody has a solution for it or am I misusing the RegExp object in javascript. I've written down a regexp which checks whether a particular value is alphanumeric or not. The function and some sample test cases are as follows

var re = new RegExp("^[a-zA-z\\d]+$");

document.writeln(re.test("a")); 
document.writeln(re.test("a1234")); 
document.writeln(re.test("12345a"));
document.writeln(re.test("12345"));
document.writeln(re.test("a["));
document.writeln(re.test("[]"));
document.writeln(re.test("]"));

In all the cases, it returns a true. I tried escaping the brackets in the regular exp ie var re = new RegExp("^\\\\[a-zA-z\\\\d\\\\]+$"); but then every test case returns false.

I fixed this problem by using a regex literal instead like var re = /^[a-zA-Z\\d]+$/; . I think I could have used \\w but the field should not contain the _ character.

Does anybody know how to fix the problem or is the RegExp object not compatible with a set of matching characters??

Thanks in advance!

Answer 1

The second 'z' should be 'Z'. The ascii range between Z (0x5a) and a (0x61) includes the square brackets, the caret, backquote, and underscore.