substr_count.js

function substr_count (haystack, needle, offset, length) {
    // http://kevin.vanzonneveld.net
    // +   original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
    // +   bugfixed by: Onno Marsman
    // +   improved by: Brett Zamir (http://brett-zamir.me)
    // *     example 1: substr_count('Kevin van Zonneveld', 'e');
    // *     returns 1: 3
    // *     example 2: substr_count('Kevin van Zonneveld', 'K', 1);
    // *     returns 2: 0
    // *     example 3: substr_count('Kevin van Zonneveld', 'Z', 0, 10);
    // *     returns 3: false
    var pos = 0,
        cnt = 0;

    haystack += '';
    needle += '';
    if (isNaN(offset)) {
        offset = 0;
    }
    if (isNaN(length)) {
        length = 0;
    }
    offset--;

    while ((offset = haystack.indexOf(needle, offset + 1)) != -1) {
        if (length > 0 && (offset + needle.length) > length) {
            return false;
        }
        cnt++;
    }

    return cnt;
}