在js中不存在private 私有变量的定义,但利用闭包可以模拟
var getter, setter;
(function(){
var privateA = 0;
getter = function(){
return privateA;
};
setter = function(newVal){
if(typeof newVal != 'number'){
throw new Error("不是number")
}
privateA = newVal;
}
})();