How to use the jszip.apply function in jszip

function EasyZip() {
    JSZip.apply(this, arguments);
    this.clone = function() {
        var newObj = new EasyZip();
        for (var i in this) {
            if (typeof this[i] !== "function") {
                newObj[i] = this[i];
            }
        }
        return newObj;
    };
}