是否可以在ES6类中创建私有属性?
举个例子。 如何阻止访问instance.property?
class Something {
constructor(){
this.property = "test";
}
}
var instance = new Something();
console.log(instance.property); //=> "test"
是否可以在ES6类中创建私有属性?
举个例子。 如何阻止访问instance.property?
class Something {
constructor(){
this.property = "test";
}
}
var instance = new Something();
console.log(instance.property); //=> "test"
当前回答
我现在听到的建议是使用WeakMaps来保存私人数据,以供其他看客参考。
下面是一个更清晰、有效的例子:
function storePrivateProperties(a, b, c, d) {
let privateData = new WeakMap;
// unique object as key, weak map can only accept object as key, when key is no longer referened, garbage collector claims the key-value
let keyA = {}, keyB = {}, keyC = {}, keyD = {};
privateData.set(keyA, a);
privateData.set(keyB, b);
privateData.set(keyC, c);
privateData.set(keyD, d);
return {
logPrivateKey(key) {
switch(key) {
case "a":
console.log(privateData.get(keyA));
break;
case "b":
console.log(privateData.get(keyB));
break;
case "c":
console.log(privateData.get(keyC));
break;
case "d":
console.log(privateData.set(keyD));
break;
default:
console.log(`There is no value for ${key}`)
}
}
}
}
其他回答
我现在听到的建议是使用WeakMaps来保存私人数据,以供其他看客参考。
下面是一个更清晰、有效的例子:
function storePrivateProperties(a, b, c, d) {
let privateData = new WeakMap;
// unique object as key, weak map can only accept object as key, when key is no longer referened, garbage collector claims the key-value
let keyA = {}, keyB = {}, keyC = {}, keyD = {};
privateData.set(keyA, a);
privateData.set(keyB, b);
privateData.set(keyC, c);
privateData.set(keyD, d);
return {
logPrivateKey(key) {
switch(key) {
case "a":
console.log(privateData.get(keyA));
break;
case "b":
console.log(privateData.get(keyB));
break;
case "c":
console.log(privateData.get(keyC));
break;
case "d":
console.log(privateData.set(keyD));
break;
default:
console.log(`There is no value for ${key}`)
}
}
}
}
哦,这么多奇异的解决方案!我通常不关心隐私,所以我使用“伪隐私”,正如这里所说的。但如果确实关心(如果有一些特殊的要求),我会在这个例子中使用:
class jobImpl{
// public
constructor(name){
this.name = name;
}
// public
do(time){
console.log(`${this.name} started at ${time}`);
this.prepare();
this.execute();
}
//public
stop(time){
this.finish();
console.log(`${this.name} finished at ${time}`);
}
// private
prepare(){ console.log('prepare..'); }
// private
execute(){ console.log('execute..'); }
// private
finish(){ console.log('finish..'); }
}
function Job(name){
var impl = new jobImpl(name);
return {
do: time => impl.do(time),
stop: time => impl.stop(time)
};
}
// Test:
// create class "Job"
var j = new Job("Digging a ditch");
// call public members..
j.do("08:00am");
j.stop("06:00pm");
// try to call private members or fields..
console.log(j.name); // undefined
j.execute(); // error
函数(构造函数)的另一种可能实现:
function Job(name){
var impl = new jobImpl(name);
this.do = time => impl.do(time),
this.stop = time => impl.stop(time)
}
我用这个模式,它总是对我有效
class Test { constructor(data) { class Public { constructor(prv) { // public function (must be in constructor on order to access "prv" variable) connectToDb(ip) { prv._db(ip, prv._err); } } // public function w/o access to "prv" variable log() { console.log("I'm logging"); } } // private variables this._data = data; this._err = function(ip) { console.log("could not connect to "+ip); } } // private function _db(ip, err) { if(!!ip) { console.log("connected to "+ip+", sending data '"+this.data+"'"); return true; } else err(ip); } } var test = new Test(10), ip = "185.167.210.49"; test.connectToDb(ip); // true test.log(); // I'm logging test._err(ip); // undefined test._db(ip, function() { console.log("You have got hacked!"); }); // undefined
使用WeakMap可以在类中拥有私有方法。
根据MDN网络文档:
WeakMap对象是键/值对的集合,其中键仅为对象,值可以是任意值。 键中的对象引用是弱保存的,这意味着如果不再有对该对象的其他引用,则它们是垃圾收集(GC)的目标。
这是一个创建带有私有成员_items的Queue数据结构的例子,该成员_items包含一个数组。
const _items = new WeakMap();
class Queue {
constructor() {
_items.set(this, []);
}
enqueue( item) {
_items.get(this).push(item);
}
get count() {
return _items.get(this).length;
}
peek() {
const anArray = _items.get(this);
if( anArray.length == 0)
throw new Error('There are no items in array!');
if( anArray.length > 0)
return anArray[0];
}
dequeue() {
const anArray = _items.get(this);
if( anArray.length == 0)
throw new Error('There are no items in array!');
if( anArray.length > 0)
return anArray.splice(0, 1)[0];
}
}
使用的例子:
const c = new Queue();
c.enqueue("one");
c.enqueue("two");
c.enqueue("three");
c.enqueue("four");
c.enqueue("five");
console.log(c);
私有成员_items是隐藏的,不能在Queue对象的属性或方法中看到:
然而,Queue对象中的私有成员_items可以通过以下方式访问:
const anArray = _items.get(this);
答案是“不”。但是你可以像这样创建对属性的私有访问:
使用模块。模块中的所有内容都是私有的,除非使用export关键字将其设为公有。 在模块内部,使用函数闭包:http://www.kirupa.com/html5/closures_in_javascript.htm
(可以使用符号来确保隐私的建议在ES6规范的早期版本中是正确的,但现在不再是这样:https://mail.mozilla.org/pipermail/es-discuss/2014-January/035604.html和https://stackoverflow.com/a/22280202/1282216。有关符号和隐私的详细讨论,请参阅:https://curiosity-driven.org/private-properties-in-javascript)