使用函数构造函数覆盖 Object.prototype 方法时出现范围错误 [英] Range error when overriding Object.prototype method with Function constructor
问题描述
我试图覆盖 Object.prototype.toString
以添加额外类描述的功能.
I'm trying to override Object.prototype.toString
in a bid to add functionality for additional class descriptions.
这是初始代码:
(function(toString){
Object.prototype.toString = function(){
if(this instanceof TestClass)
{
return '[object TestClass]';
}
return toString.apply(this, arguments);
}
})(Object.prototype.toString);
function TestClass(){}
var instance_obj = new TestClass();
Object.prototype.toString.call(instance_obj);
当我在控制台中运行它时,我得到以下输出:
When I run this in the console, I get the following output:
[object TestClass]
好消息是它不会彻底改变 Object.prototype.toString
的工作方式,所以使用另一种类型 [即不是 TestClass],事情按预期工作,例如Object.prototype.toString.call(12)
会输出[object Number]
.
The good thing is that it doesn't drastically modify the way Object.prototype.toString
works, so with another type [i.e. not TestClass], things work just as expected e.g. Object.prototype.toString.call(12)
will output [object Number]
.
到目前为止,此实现没有任何问题.但是,我有以下代码的另一个实现:
This implementation works with no issues so far. However, I have another implementation with the following code:
(function(toString){
var fn_code_str = `return function(){
if(this instanceof TestClass)
{
return '[object TestClass]';
}
return toString.apply(this, arguments);
}`;
var pre_fn = new Function(fn_code_str);
Object.prototype.toString = pre_fn();
})(Object.prototype.toString);
function TestClass(){}
var instance_obj = new TestClass();
Object.prototype.toString.call(instance_obj);
有了这个,我得到了 TestClass 的正确输出,但是当我使用其他东西时,比如 12
,我得到一个 RangeError:
With this, I get the proper output for TestClass, but when I use something else, like 12
, I get a RangeError:
VM527:5 Uncaught RangeError: Maximum call stack size exceeded
at Function.[Symbol.hasInstance] (<anonymous>)
at Number.eval (eval at <anonymous> (getElements.html:19), <anonymous>:5:21)
at Number.eval (eval at <anonymous> (getElements.html:19), <anonymous>:10:29)
at Number.eval (eval at <anonymous> (getElements.html:19), <anonymous>:10:29)
at Number.eval (eval at <anonymous> (getElements.html:19), <anonymous>:10:29)
at Number.eval (eval at <anonymous> (getElements.html:19), <anonymous>:10:29)
at Number.eval (eval at <anonymous> (getElements.html:19), <anonymous>:10:29)
at Number.eval (eval at <anonymous> (getElements.html:19), <anonymous>:10:29)
at Number.eval (eval at <anonymous> (getElements.html:19), <anonymous>:10:29)
at Number.eval (eval at <anonymous> (getElements.html:19), <anonymous>:10:29)
这似乎是 toString.apply
的递归问题.但是,我不明白为什么第二个实现是递归的,如果第一个没有?
This appears to be an issue with recursion of toString.apply
. However, I can't figure out why this second implementation is recursing, if the first one does not?
注意:第二个实现的原因是添加类型检查代码[即if(this instanceof MyClassType){return '[object MyClassType]'}
] 从数组中的类名列表中动态返回不同的类.换句话说,不是为我想出的每个新类修改代码,而是将类名附加到数组中,然后自动生成条件语句.
Note: The reason for this second implementation is to add the type-checking code [i.e. if(this instanceof MyClassType){return '[object MyClassType]'}
] for different classes dynamically from a list of class names in an array. In other words, rather than modifying code for each new Class I come up with, I append the class name to the array instead, and the conditional statement is generated automatically.
推荐答案
问题是您的 IIFE 的 toString
参数不在您的 new Function
代码范围内.相反,它使用全局 toString
= window.toString
= Object.prototype.toString
.
The problem is that the toString
parameter of your IIFE is not in scope in your new Function
code. Instead, it uses the global toString
= window.toString
= Object.prototype.toString
.
要解决这个问题,您需要在 new Function
的代码中声明 toString
变量,以使返回的闭包起作用.或者作为一个简单的常量:
To fix this, you need to declare the toString
variable inside the new Function
's code to make the returned closure work. Either as a simple constant:
(function() {
var pre_fn = new Function(`
const toString = Object.prototype.toString;
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
return function(){
if(this instanceof TestClass) {
return '[object TestClass]';
}
return toString.apply(this, arguments);
}`);
Object.prototype.toString = pre_fn();
})();
或作为参数:
(function() {
var pre_fn = new Function('toString', `
// ^^^^^^^^^^^
return function(){
if(this instanceof TestClass) {
return '[object TestClass]';
}
return toString.apply(this, arguments);
}`);
Object.prototype.toString = pre_fn(Object.prototype.toString);
// ^^^^^^^^^^^^^^^^^^^^^^^^^
})();
这篇关于使用函数构造函数覆盖 Object.prototype 方法时出现范围错误的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!