在Javascript中通过引用传递字符串 [英] Pass a string by reference in Javascript

问题描述

我想创建一个字符串并通过引用传递它，以便我可以更改单个变量并将其传播到引用它的任何其他对象。

I want to create a string and pass it by reference such that I can change a single variable and have that propagate to any other object that references it.

Take这个例子：

function Report(a, b) {
    this.ShowMe = function() { alert(a + " of " + b); }
}

var metric = new String("count");
var a = new Report(metric, "a"); 
var b = new Report(metric, "b"); 
var c = new Report(metric, "c"); 
a.ShowMe();  // outputs:  "count of a";
b.ShowMe();  // outputs:  "count of b";
c.ShowMe();  // outputs:  "count of c";

我希望能够实现这一目标：

I want to be able to have this happen:

var metric = new String("count");
var a = new Report(metric, "a"); 
var b = new Report(metric, "b"); 
var c = new Report(metric, "c"); 
a.ShowMe();  // outputs:  "count of a";
metric = new String("avg");
b.ShowMe();  // outputs:  "avg of b";
c.ShowMe();  // outputs:  "avg of c";

为什么这不起作用？

MDC对字符串的引用表示度量标准是一个对象。

The MDC reference on strings says metric is an object.

我试过这个，这不是我想要的，但非常接近：

I've tried this, which is not what I want, but is very close:

var metric = {toString:function(){ return "count";}};
var a = new Report(metric, "a"); 
var b = new Report(metric, "b"); 
var c = new Report(metric, "c"); 
a.ShowMe();  // outputs:  "count of a";
metric.toString = function(){ return "avg";}; // notice I had to change the function
b.ShowMe();  // outputs:  "avg of b";
c.ShowMe();  // outputs:  "avg of c";

alert(String(metric).charAt(1)); // notice I had to use the String constructor
// I want to be able to call this: 
// metric.charAt(1)

这里的重点：

1. 我希望能够使用指标喜欢它是普通的字符串对象


2. 我希望每个报告都引用同一个对象。

1. I want to be able to use metric like it's a normal string object
2. I want each report to reference the same object.

推荐答案

Javascript中的字符串已经通过引用传递 - 使用字符串调用过程不涉及复制字符串的内容。手头有两个问题：

Strings in Javascript are already passed "by reference" -- calling a procedure with a string does not involve copying the string's contents. There are two issues at hand:

• 字符串是不可变的。与C ++字符串相反，一旦创建了JavaScript字符串，就无法对其进行修改。


• 在JavaScript中，变量不是像C ++中那样静态分配的插槽。在您的代码中， metric 是一个适用于两个完全独立的字符串变量的标签。

• Strings are immutable. In contrast to C++ strings, once a JavaScript string has been created it cannot be modified.
• In JavaScript, variables are not statically assigned slots like in C++. In your code, metric is a label which applies to two entirely separate string variables.

这是实现目标的一种方法，使用闭包来实现 metric 的动态范围：

Here's one way to achieve what you want, using closures to implement dynamic scoping of metric:

function Report(a, b) {
    this.ShowMe = function() { alert(a() + " of " + b); }
}

var metric = "count";
var metric_fnc = function() { return metric; }
var a = new Report(metric_fnc, "a"); 
var b = new Report(metric_fnc, "b"); 
a.ShowMe();  // outputs:  "count of a";
metric = "avg";
b.ShowMe();  // outputs:  "avg of b";

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