javascript - JavaScript 中的 void、eval 和 Function 构造函数有什么区别？

Question

void(document.body.innerText += 'hi')

eval(document.body.innerText +='\nbye')

Function(document.body.innerText += '\n!!!')

void(Function(function foo(){document.body.innerText += '\n>hi2'; return true}).toString())();

eval(Function(function foo(){document.body.innerText += '\nbye2'; return true}).toString())();

Function(Function(function foo(){document.body.innerText += '\n!!!2'; return true}).toString())();

在这些不同的语句中执行代码的处理模型是什么？

void(alert('hi'))
undefined

eval(alert('hi'))
undefined

Function(alert('hi'))
function anonymous() {
  undefined
}

eval(Function(function foo(){return true}).toString())();
TypeError: undefined is not a function

void(Function(function foo(){return true}).toString())();
TypeError: string is not a function

Function(Function(function foo(){return true}).toString())();
undefined

Answer 1

在this article eval 和 Function 构造函数解释如下:

(…) Global, built-in eval function evaluates code in the scope of a caller.

The code executed from within function created by Function constructor doesn’t really execute in global scope. However, it doesn’t execute in local scope either, which is what probably leads to confusion. Function constructor creates a function whose scope chain consists of nothing but a global scope (preceded with function’s own Activation Object, of course). Any code contained in a function created via Function constructor evaluates in a scope of that function, not in a global scope. However, it’s almost as if code executes globally, since global object is the very next object in the scope chain.

并根据this page , void 只返回 undefined:

In many languages, void is a type that has no values. In JavaScript, void is an operator that takes an operand and returns undefined. This is not useful, and it is very confusing. Avoid void.