为什么EcmaScript 5严格模式会限制标识符“eval” [英] Why does EcmaScript 5 strict mode go to such great lengths to restrict the identifier `eval`

问题描述

根据规范（附件C），严格模式代码几乎不能做任何可能分配名称 eval 的任何标识符的事情。我可以理解，人们可能想要限制使用实际的 eval 函数，但是我没有看到限制使用这个名字？

According to the spec (Annex C), strict-mode code can't do pretty much anything that might assign any identifier with the name eval. I can understand that one might want to restrict use of the actual eval function, but I don't see what purpose is served by restricting use of the name?

推荐答案

我只能推测，但在我看来，ES5严格说的是 eval 和参数应被视为原始语法，而不是标识符。这两个特征应该在语法层面实现是合理的，因为它们具有神奇的Funky Magic行为，这些行为无法通过正常函数再现。

I can only speculate, but it seems to me that ES5-strict is saying that eval and arguments should be considered as raw syntax, not identifiers. It is reasonable that these two features should be implemented at the syntactical level, because they have Amazing Funky Magic behaviours that cannot be reproduced by a normal function.

（特别是 eval 可以写入调用它的函数中的局部变量，并写入 arguments 奇怪地改变对应的局部变量的值谢天谢地，虽然这种行为似乎在严格模式下消失了。）

(In particular eval may write to local variables in the function that calls it, and writing to arguments bizarrely changes the values of local variables corresponding to the arguments. Though this behaviour seems to be going away in strict mode, thankfully.)

出于兼容性原因，ES5实际上无法生成 eval 和参数语法。所以他们尽可能地做到最近，也就是说标识符 arguments 总是引用 arguments magic和标识符 eval 总是专门指 eval magic。

For compatibility reasons, ES5 can't actually make eval and arguments syntactical. So they do the nearest they can, which is to say that the identifier arguments always refers to arguments magic and the identifier eval always exclusively refers to eval magic.

它如果JS引擎可以确定函数是否包含魔法，那么也可以提高优化的可能性。

It could also improve the possibilities for optimisation, if JS engines can be sure whether a function contains magic.

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