Function expression hoisting?

Question

Source: https://developer.mozilla.org/el/docs/Web/JavaScript/Reference/Operators/function
"Function expressions in JavaScript are not hoisted, unlike function declarations. You can't use function expressions before you declare them."

Example:

var hey = function(){
    console.log("hi");
}

Chrome's console: window.hey returns

function (){
console.log("hi");
}

I don't see any question here, pls make clear what you want to know. — cyr_x, Mar 06 '17 at 00:20
What's the question? You're using `window.hey` **after** you declare the function, so the dociumentation you quoted doesn't apply. — Barmar, Mar 06 '17 at 00:20
I guess the word "hoisting" is unclear to him. `function x()` can be called even prior to its declaration, while `var x = function()` is not available until it's defined. — Psi, Mar 06 '17 at 00:21

score 1 · Answer 1 · edited May 23 '17 at 12:25

What it's saying is that you can't write:

hey();
var hey = function() {
    console.log("hi");
}

because you're using the variable hey before you assign the function expression to it. But you can write:

hey();
function hey() {
    console.log("hi");
}

because function declarations are hoisted to the beginning of the containing function.

score 0 · Answer 2 · answered Mar 06 '17 at 01:12

To build on @Barmar's answer, when you do:

hey();
var hey = function() {
    console.log("hi");
}

technically the variable declaration is still hoisted, but the assignment remains where it is written, so it is equivalent to:

var hey;
hey(); // hey is declared as a variable, but is still undefined.
hey = function() {
    console.log("hi");
}

2 Answers2