Does V8 cache compiled regular expressions automatically?

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?

Well, let's find out.

function isFooBar(str) {
  return 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}
console.time('1');isFooBar("Foo");console.timeEnd('1');
console.time('2');isFooBar("Bar");console.timeEnd('2');

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

(Regex from Complex password Regular expression)

So, I guess the answer to your question is YES, V8 automatically caches the regex.

http://code.google.com/p/v8/issues/detail?id=933#c3

In Chrome 9 we have removed a primitive caching of RegExp results. That means that we no longer take unrealistically low time for repeating the same operation on the same input over and over again. The caching was originally added to make a point about benchmarks that were too simplistic (our own, at that time, included) being too easy to "game" by adding such caching (which makes no difference in real-world scenarios). Most benchmarks have since improved so much that we decided to remove the caching (and its unavoidable overhead). The cache was added in v8 revision 4083 (released in Chrome 5) and removed in revision 5755 (will be in Chrome 9)