Regular expressions can be created via the RegExp constructor.
It accepts two arguments: a string pattern and an optional string of flags.
Any regular expression that can be defined using literal syntax can be defined using the constructor:
The following Regular expressions match the first instance of "bat" or "cat", regardless of case.
var pattern1 = /[bc]at/i;
Same as pattern1, using the constructor.
var pattern2 = new RegExp("[bc]at", "i");
Since the argument of the RegExp constructor is a string, you need to escape characters.
All metacharacters must be double-escaped, \\ becomes \\\\ when used in a regular-expression string.
var re = null, i;/* w ww . j a v a2 s .c om*/ re = new RegExp("cat", "g"); console.log(re.test("catastrophe"));