function Utils() {
    if(typeof Utils.initialized == "undefined"){
        console.log("prototype init");
        Utils.prototype.utilsFunc1 = function () {
            console.log("utilsFunc1");
        };
        Utils.prototype.utilsFunc2 = function () {
            console.log("utilsFunc2");
        };
    }
    Utils.initialized =true;
}

var instance1 = new Utils();
instance1.utilsFunc1();
var instance2 = new Utils();
instance2.utilsFunc1();

“prototype init ” 只打印一次