Alert is not displaying as expected.!

Question

I just tried to check the scope variation by using the following code, but the result is coming not in an expected way. Can anyone explain what's going on exactly behind this..?

var a = 10;

+ function () {
  a = 5;
  var a;
  alert("inline  " + a); //Expected undefined but it displayed as 5
}();

alert(a); //Expected 5 but it alerted 10

DEMO

@RPM yeah.. but this confuses me.. http://jsfiddle.net/3rCYz/4/ — Balachandran, May 27 '14 at 05:01
Javascript function only have local and global scope. Anything (variable/method) which is declared inside a function/method has local scope. And variable which is declared outside the function/method has global scope. — Mohit Pandey, May 27 '14 at 05:11
possible duplicate of [JavaScript 'hoisting'](http://stackoverflow.com/questions/15311158/javascript-hoisting) — Qantas 94 Heavy, Sep 26 '14 at 10:51

score 2 · Accepted Answer · edited Jul 23 '14 at 05:44

var hoisting

Because variable declarations (and declarations in general) are processed before any code is executed, declaring a variable anywhere in the code is equivalent to declaring it at the top. This also means that a variable can appear to be used before it's declare

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/var

The compiler understands your code as

var a;
a = 5;

score 2 · Answer 2 · answered May 27 '14 at 05:02

2

The position of a var declaration within a function doesn't matter. These are entirely equivalent:

function () {
    var a;
    a = 5;
}

function () {
    a = 5;
    var a;
}

answered May 27 '14 at 05:02

Chris Martin

30,334
10
78
137

score 0 · Answer 3 · answered May 27 '14 at 05:05

0

when use "var a" you request global value of variable, use "window.a" to display it:

<script>
var a = 10;

+ function () {
    a = 5;
    var a;
    alert("inline  " + window.a); //Expected undefined but it displayed as 5
}();

</script>

answered May 27 '14 at 05:05

mwafi

3,946
8
56
83

score -1 · Answer 4 · edited May 27 '14 at 05:07

-1

var a = 10; // Global scope

+ function () {
    a = 5; // You are not using Var here .. so it is also a global scope
    var a; // Now you are mentioning your a is Var so scope is changed from global to this function
    alert("inline  " + a); // Printing 5 because you local scope a has value of 5.
}();

alert(a); // Printing 10 because of global scope a has value 10

edited May 27 '14 at 05:07

Rajaprabhu Aravindasamy

66,513
17
101
130

answered May 27 '14 at 05:05

Bluewings

3,438
3
18
31

Alert is not displaying as expected.!

DEMO

4 Answers4