在Javascript中实现私有实例变量 [英] Implementing private instance variables in Javascript

问题描述

我不知道我多久都错过了这个。我一直假设私有实例变量像这样工作，但他们没有。当然，它们是私有的（如非全局的），但变量是跨实例共享的。这导致了一些非常令人困惑的错误。

I don't know how I've missed this for so long. I've been presuming private instance variables to work like this, but they don't. They're private (as in non-global), certainly, but the variables are shared across instances. This led to some very confusing bugs.

我认为我正在遵循一些最好的库实现的最佳实践，但似乎我错过了一些东西。

I thought I was following the best practices implemented by some of the best libraries out there, but it seems I missed something.

var Printer = (function(){
    var _word;

    Printer = function(word){
        _word = word;
    }

    _print = function(){
        console.log(_word);
    }

    Printer.prototype = {
        print: _print
    }
    return Printer;
})();

var a = new Printer("Alex");
var b = new Printer("Bob");

a.print(); //Prints Bob (!)
b.print(); //Prints Bob

我看过这篇文章，但它没有描述最佳实践实现私有实例变量。 （这甚至是我想要的名字吗？）
JavaScript中私有变量和实例变量的方法和变量范围

I have looked at this post, but it doesn't describe a best practice for implementing private instance variables. (is this even the name of what I want?) Method and variable scoping of private and instance variables in JavaScript

我也查看了这篇文章，但是使用'this '关键字是我以前做的。因为它没有混淆我试图避免它。这真的是唯一的方法吗？
在原型继承中实现实例方法/变量

I also looked at this post, but the use of the 'this' keyword is what I used to do. Because it doesn't obfuscate I was trying to avoid it. Is this really the only way? Implementing instance methods/variables in prototypal inheritance

推荐答案

你正在做那个关闭的好东西。 _word 需要在 Printer 函数中声明，而不是在匿名封闭的土地中丢失：

You're doing some wonky stuff with that closure. _word needs to be declared in the Printer function, not lost in anonymous-closure land:

function Printer(word) {
    var _word = word;

    this.print = function () {
        console.log(_word);
    }
}

var a = new Printer("Alex");
var b = new Printer("Bob");

a.print(); //Prints Alex
b.print(); //Prints Bob

这保持 _word private ，代价是在每个 Printer 实例上创建一个新的 print 函数。要降低此成本，您需要公开 _word 并在原型上使用单个 print 函数：

This keeps _word private, at the expense of creating a new print function on every Printer instance. To cut this cost, you expose _word and use a single print function on the prototype:

function Printer(word) {
    this._word = word;
}

Printer.prototype.print = function () {
    console.log(this._word);
}

var a = new Printer("Alex");
var b = new Printer("Bob");

a.print(); //Prints Alex
b.print(); //Prints Bob

真的 是否重要 _word 是否已曝光？就个人而言，我不这么认为，特别是考虑到 _ 前缀。

Does it really matter that _word is exposed? Personally, I don't think so, especially given the _ prefix.

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