javascript - ReferenceError: variable is not defined

Question

I met this issue sometimes but still don't know what causes it.

I have this script in the page:

$(function(){
    var value = "10";
});

But the browser says "ReferenceError: value is not defined". However if I go to the browser console and input either

10

or

var value = "10";

either of them can return 10. What is the problem with my script?

Answer 1

It's declared inside a closure, which means it can only be accessed there. If you want a variable accessible globally, you can remove the var:

$(function(){
    value = "10";
});
value; // "10"

This is equivalent to writing window.value = "10";.