非递归地替换内置的 javascript 函数

发布于 2024-10-18 05:51:58 字数 311 浏览 1 评论 0原文

我在这里写了一些书签，我有一些与内置 javascript 函数相关的问题。

假设我想替换内置提示功能（不一定在书签中）。这看起来很简单，但是有没有办法从这个替换中调用内置提示函数？

prompt = function(message){
    var tmp = prompt(message);
    hook(tmp);
    return tmp;
}

我无法正确确定范围；这个例子产生无限递归。

还有一种方法可以恢复已被替换的内置 javascript 函数的默认行为（无需附加额外的引用）。

原文

I am writing some bookmarklets here and I have some questions related to built-in javascript functions.

Let's say I want to replace the built-in prompt function (not necessarily in a bookmarklet). That seems easy enough, but is there a way to call the builtin prompt function from within this replacement?

prompt = function(message){
    var tmp = prompt(message);
    hook(tmp);
    return tmp;
}

I couldn't get the scoping to work out right; this example yields infinite recursion.

Also is there a way to restore the default behavior of a builtin javascript function that has been replaced (without hanging on to an extra reference).

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夏见 2024-10-25 05:51:58

(function () {
    var old_prompt = prompt;
    prompt = function (msg) {
        var tmp = old_prompt(msg);
        hook(tmp);
        return tmp;
    };
    prompt.restore = function () { prompt = old_prompt; }
    // analogous for other functions you want to replace
})();

将其包装在（自动执行）函数中可确保 old_prompt 不会泄漏到外部。不过，您确实需要公开一些东西。我选择提供一个进行恢复的函数，是为了方便，也许，可以说，是面向未来和封装的。只要高阶函数避免摆弄其他人的范围...

另外，不，（我假设）不可能在没有任何引用的情况下恢复变量的先前值（旧值），即使该值恰好是内置的。即使有可能，这也会是一个相当晦涩的技巧——这种方法有效，所以让我们坚持下去。

（func.restore 归功于 Martijn）

(function () {
    var old_prompt = prompt;
    prompt = function (msg) {
        var tmp = old_prompt(msg);
        hook(tmp);
        return tmp;
    };
    prompt.restore = function () { prompt = old_prompt; }
    // analogous for other functions you want to replace
})();

Wrapping it up in a (self-executing) function ensures that old_prompt doesn't leak to the outside. You do need to expose something though. I chose to provide a function doing the restoring, for convenience and perhaps, one could say, future-proofing and encapsulation. As long as higher order functions refrain from fiddling with someone else's scope...

Also, no, it's (I'd assume) not possible to restore the previous value of a variable without any reference to it (the old value), even if that value happened to be a built-in. Even if it was possible, it'd be a pretty obscure trick - this way works, so let's just stick with it.

(Credit for func.restore goes to Martijn)

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