相关疑难解决方法(0)

考虑以下JavaScript代码(在节点REPL中):

> let a = new Array(10)
undefined
> a
[ <10 empty items> ]
> a.map(e => 1)
[ <10 empty items> ]
> let b = new Array(10).fill(undefined)
undefined
> b
[ undefined,
  undefined,
  undefined,
  undefined,
  undefined,
  undefined,
  undefined,
  undefined,
  undefined,
  undefined ]
> b.map(e => 1)
[ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 ]
> 

当我创建一个空数组时,我会得到"空项",它们的行为似乎与之不同undefined.有人能解释一下有什么区别吗？