你可以在声明后更改 Javascript 函数吗? [英] Can you alter a Javascript function after declaring it?

问题描述

假设我有 var a = function() { return 1;}.是否可以更改 a 以便 a() 返回 2?也许通过编辑 a 对象的属性，因为 每个函数是一个对象?

Let's say I have var a = function() { return 1; }. Is it possible to alter a so that a() returns 2? Perhaps by editing a property of the a object, since every function is an object?

更新:哇，谢谢大家的回复.但是，恐怕我不想简单地重新分配变量，而是实际编辑现有函数.我正在考虑如何组合 部分函数 在 Scala 中创建一个新的 PartialFunction.我有兴趣在 Javascript 中编写类似的东西，并认为现有的函数也许可以更新，而不是创建一个全新的 Function 对象.

Update: Wow, thanks for all the responses. However, I'm afraid I wasn't looking to simply reassign a variable but actually edit an existing function. I am thinking along the lines of how you can combine partial functions in Scala to create a new PartialFunction. I am interested in writing something similar in Javascript and was thinking that the existing function could perhaps be updated, rather than creating an entirely new Function object.

推荐答案

你可以用 javascript 做各种有趣的事情，包括重新定义函数:

You can do all kinds of fun stuff with javascript, including redefining functions:

let a = function() { return 1; }
console.log(a()); // 1
    
// keep a reference
let old = a;
   
// redefine
a = function() {
  // call the original function with any arguments specified, storing the result
  const originalResult = old.apply(old, arguments);
  // add one
  return originalResult + 1;
};

console.log(a()); // 2

瞧.

更新以在更疯狂的场景中显示:

Updated to show this in a crazier scenario:

let test = new String("123");
console.log(test.toString()); // logs 123
console.log(test.substring(0)); // logs 123
String.prototype.substring = function(){ return "hahanope"; }
console.log(test.substring(0)); // logs hahanope

您可以在这里看到即使测试"首先定义，然后我们重新定义 substring()，更改仍然适用.

You can see here that even though "test" is defined first, and we redefine substring() afterwards, the change still applies.

旁注:如果你这样做，你真的应该重新考虑你的架构......当他/她正在查看一个应该的函数定义时，你会在 5 年后混淆一些可怜的开发人员的废话返回 1，但似乎总是返回 2....

Side note: you really should reconsider your architecture if you're doing this...you're going to confuse the crap out of some poor developer 5 years down the road when s/he's looking at a function definition that's supposed to return 1, but seems to always return 2....

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