Does V8 cache compiled regular expressions automatically?

Question

So I know that in Javascript instantiating a regex causes it to be compiled automatically and if that regex is stored in a variable it will be reused without recompiling. Example:

var re = /[Ff]oo|[Bb]ar/;
"Foo".match(re); // ["Foo"]
"Baz".match(re); // null

However, are duplicated regular expressions recompiled or does V8 (Chrome/Node.js) intelligently re-use them (like PHP does with preg_* functions)?

function isFooBar(str) {
  return str.match(/[Ff]oo|[Bb]ar/);
}
isFooBar("Foo"); // ["Foo"]
isFooBar("Baz"); // null

So to clarify, I know the first example results in one compilation of the regex. But what about the second example?

Answer 1

Well, let's find out.

// http://stackoverflow.com/questions/3466850/complex-password-regular-expression
function isFooBar(str) {
  return str.match(/^(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(?:(?=.*[a-z])(?:(?=.*[A-Z])(?=.*[\d\W])|(?=.*\W)(?=.*\d))|(?=.*\W)(?=.*[A-Z])(?=.*\d)).{8,}(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$)?(^(?=.*\d)(?=.*[a-z])(?=.*[@#$%^&+=]).*$)?(^(?=.*\d)(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?(^(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)?$/);
}
console.time('1');isFooBar("Foo");console.timeEnd('1');
console.time('2');isFooBar("Bar");console.timeEnd('2');

(Open your console and run the code snippet above to see if the results for your browser.)

On Node.js 0.10.36 (V8 3.14.5.9):

1: 65ms
2: 0ms

On io.js 1.6.3 (V8 4.1.0.27):

1: 32ms
2: 0ms

So, I guess the answer to your question is YES, V8 is capable of automatically caching the regex.

---

EDIT:

Even though V8 is capable of such optimization, it might not in fact choose to always use this optimization. V8 has many complex heuristics for different cases, like when to inline a function, when to optimize a function, when to de-optimize a function, etc. Unless you are a V8 developer, many of these heuristics would appear to be bizarre or unexpected or both.

Not being a V8 developer myself, I do not know the answer to the specific question or if regexes are always automatically cached. However, even if I do know the answer, it may change in the future. So when you are writing code, I would still recommend storing the regex in such a way that it is clear what the intention for this variable is. And for the example above, this means lifting the regex variable out of the function isFooBar().

Another issue is how this regex is created. The example above and in OP's question are declared with a regular expression literal. However, if you are using the new RegExp() constructor, V8 would not be allowed to cache the regex since it might change during runtime.