javascript - 为什么全局let变量没有添加到浏览器的window对象中？

Question

这个问题已经有答案了:

why don't const and let statements get defined on the window object [duplicate] (2 个回答)

已关闭 3 年前。

考虑下面我在 Chrome 浏览器控制台中运行的代码:

var x = "hello";

let foo =  function(){
  console.log("hi");
};

console.log(x); // hello
console.log(foo()); //hi

console.log(window.x); // hello
console.log(window.foo()); // Error

如果我使用var foo =...而不是let foo = ..那么这就会起作用。为什么 ？

Answer 1

作者:design :

let allows you to declare variables that are limited to a scope of a block statement, or expression on which it is used, unlike the var keyword, which defines a variable globally, or locally to an entire function regardless of block scope. The other difference between var and let is that the latter is initialized to a value only when a parser evaluates it (see below).

Just like const the let does not create properties of the window object when declared globally (in the top-most scope).