为什么这个变量在我执行“函数MyVar（）{}”之前有一个值？

Question

I'm trying to understand why this code behaves the way it does:

test.js

var User;

console.dir(User);

function User(name) { // User = function(name) { ... seems not to be the same?
    this.name = name;
}

node test.js

[Function: User]

Why does User have a value before the function() statement?

Answer 1

Hoisting! http://www.adequatelygood.com/JavaScript-Scoping-and-Hoisting.html

var and function statements are automatically hoisted to the top of the script!

This allows functions to be used before they are defined, like this:

dothis();
function dothis() { alert('wow'); }

edit function statements like this are not affected:

myfunc(); // won't work
var myfunc = function() { alert('nope'); }

Answer 2

That function is defined at parse time.

Please refer to: var functionName = function() {} vs function functionName() {}