Question

What’s the maximum size of a regular expression in modern browsers (i.e. Firefox 3+, Safari 4+, IE 7+)? Assume a simple regular expression, of, say “foo|bar|baz|woot|…”

Answer 1

You can use this code to test, in IE8 / firefox with firebug / Chrome.

var regex = "";
var maximum = 100;
var showAfter = 95;
for(i = 1; i < maximum; i++) {
    regex += "aaaaaaaaaa";
    if (i > showAfter) {
        console.log(10 * i + " chars");
        console.log(RegExp(regex));
    }
}

When you get a error, you found the limit.

---

SIMPLE TEST

var regex = "";
var chars = 3204161;
for(i = 0; i < chars; i++) {
    regex += "a";
}
alert(chars + " chars");
var a = RegExp(regex); // don't send to console, to be faster

---

RESULTS

In Firefox 3.6.3 (Ubuntu 32 bits) I get error when I tried a regex with 9M chars (9.999.990 chars) 3.204.161 chars. With 3.204.160 it’s ok.

In Chrome 5.0.3 the limit is something between 20M and 25M chars.

The error, in firefox, is:

script stack space quota is exhausted

Note: If you did some test, please comment here.