这里打印的arguments为啥是null？

Question

var a=3,b=4;function h(a,b){return a+b};console.dir(h)function h(a.b)arguments: null  这个为啥是nullcaller: nulllength: 2name: "h"prototype:Object__proto__: function()<function scope>

Answer 1

function abc(x,y,z){ return arguments;};

console.dir(abc);

/*

abc(x, y, z)

arguments: null //没调用时没有

caller: null

length: 3  //如果要获取参数个数，应该用 length

name: "abc"

prototype: abc__proto__: ()<function scope>

*/

console.dir(abc(1,2,3));

/*

[1, 2, 3]

0: 1

1: 2

2: 3

callee: abc(x,y,z)

length: 3

*/