Bubble Sweat Bubble

// This code is in the public domain. Feel free to link back to http://jan.moesen.nu/
function sprintf() {
    if (!arguments || arguments.length < 1 || !RegExp) {
        return;
    }

    var str = arguments[0];
    var re = /([^%]*)%('.|0|\x20)?(-)?(\d+)?(\.\d+)?(%|b|c|d|u|f|o|s|x|X)(.*)/;
    var a = b = [], numSubstitutions = 0, numMatches = 0;
    while (a = re.exec(str)) {
        var leftpart = a[1], pPad = a[2], pJustify = a[3], pMinLength = a[4];
        var pPrecision = a[5], pType = a[6], rightPart = a[7];

        numMatches++;

        if (pType == '%') {
            subst = '%';
        } else {
            numSubstitutions++;
            if (numSubstitutions >= arguments.length) {
                alert('Error! Not enough function arguments (' + (arguments.length - 1) + ', excluding the string)\nfor the number of substitution parameters in string (' + numSubstitutions + ' so far).');
            }

            var param = arguments[numSubstitutions];
            var pad = '';
            if (pPad && pPad.substr(0,1) == "'") {
                pad = leftpart.substr(1,1);
            } else if (pPad) {
                pad = pPad;
            }

            var justifyRight = true;
            if (pJustify && pJustify === "-") {
                justifyRight = false;
            }

            var minLength = -1;
            if (pMinLength) {
                minLength = parseInt(pMinLength);
            }

            var precision = -1;
            if (pPrecision && pType == 'f') {
                precision = parseInt(pPrecision.substring(1));
            }

            var subst = param;
            if (pType == 'b') {
                subst = parseInt(param).toString(2);
            } else if (pType == 'c') {
                subst = String.fromCharCode(parseInt(param));
            } else if (pType == 'd') {
                subst = parseInt(param) ? parseInt(param) : 0;
            } else if (pType == 'u') {
                subst = Math.abs(param);
            } else if (pType == 'f') {
                subst = (precision > -1) ? Math.round(parseFloat(param) * Math.pow(10, precision)) / Math.pow(10, precision): parseFloat(param);
            } else if (pType == 'o') {
                subst = parseInt(param).toString(8);
            } else if (pType == 's') {
                subst = param;
            } else if (pType == 'x') {
                subst = ('' + parseInt(param).toString(16)).toLowerCase();
            } else if (pType == 'X') {
                subst = ('' + parseInt(param).toString(16)).toUpperCase();
            }
        }

        str = leftpart + subst + rightPart;
    }

    return str;
}