JavaScript函数的Typeof

Question

When I declare a function like this:

function x() { return 123 };

Then:

typeof x; //return "function"
typeof x(); //return "number"

That's ok, but once I create a variable like this:

var y = function x() { return 123 };

It becomes:

typeof y; //return "function"
typeof y(); //return "number"
typeof x; //return "undefined"
typeof x(); //return error

Why does x lose his function? Please helpp

Answer 1

Why does x lose his function?

A function declaration creates a variable of the same name in the current scope.

A named function expression does not (except in certain older versions of Internet Explorer, which is a bug).

That's just how function expressions are supposed to work.