Javascript变量捕获

Question

我在 JS 中使用 eval 时遇到了奇怪的行为。

var f = function () {
    var x = 10;

    return function () {
        eval('console.log(x);');
        window['eval']('console.log(x);');
    }
};

f()();

输出:

10
undefined:1
console.log(x);
            ^
ReferenceError: x is not defined

为什么使用 eval 显式捕获 x 而 global['eval'] 却没有？即使 global['eval'] 没有捕获 x，为什么在已经捕获 的 eval 之后无法看到x?

Answer 1

window['eval'] 在全局范围内运行，eval() 在本地范围内运行。

来自 Mozilla 的 Javascript 引用:

If you use the eval function indirectly, by invoking it via a reference other than eval, as of ECMAScript 5 it works at global scope rather than local scope; this means, for instance, that function declarations create global functions, and that the code being evaluated doesn't have access to local variables within the scope where it's being called.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval