Function count the occurrences of substring in a string

occurrences.js

/** Function that count occurrences of a substring in a string;
 * @param {String} string               The string
 * @param {String} subString            The sub string to search for
 * @param {Boolean} [allowOverlapping]  Optional. (Default:false)
 *
 * @author Vitim.us https://gist.github.com/victornpb/7736865/edit
 * @see Unit Test https://jsfiddle.net/Victornpb/5axuh96u/
 * @see http://stackoverflow.com/questions/4009756/how-to-count-string-occurrence-in-string/7924240#7924240
 */
function occurrences(string, subString, allowOverlapping) {

    string += "";
    subString += "";
    if (subString.length <= 0) return (string.length + 1);

    var n = 0,
        pos = 0,
        step = allowOverlapping ? 1 : subString.length;

    while (true) {
        pos = string.indexOf(subString, pos);
        if (pos >= 0) {
            ++n;
            pos += step;
        } else break;
    }
    return n;
}

how about "foofoofooooofo".split("foo").length

occurrences("This is very good", "", true) will give 18 which seems incorrect.

why this condition if (subString.length <= 0) return (string.length + 1);

occurrences("This is very good", "", true) will give 18 which seems incorrect.

why this condition if (subString.length <= 0) return (string.length + 1);

This is to prevent occurrences("asfsdfasdfasd", "") from looping infinitely.

It returns length+1 because:

> "abcd".match(new RegExp('', 'g'))
// ["", "", "", "", ""] (5)

Thanks for this! I would like to use your function in an open-source project. What is the license of your code?