Javascript function scope

Question

Why does the alert print 2 in the below example? var a is unknown to function n...

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>

    <title>Test Doc</title>
    <script type="text/javascript">
        var a = 1;
        function f() {
            var a = 2;
            function n() {
                alert(a);
            }
            n();
        }
        f();
    </script>
</head>

<body>


</body>
</html>

"var a is unknown to function n..." that would be the case in PHP. Luckily JavaScript is not PHP. — Tomalak
– Tomalak, Commented Sep 12, 2011 at 5:22

alex · Accepted Answer · 2011-09-12 05:24:35Z

5

JavaScript functions inherit their parent's scope. Inner variables shadow parent scope variables with the same name.

1 Comment

Ray Toal Over a year ago

+1 Spot on and good link. @user443946, search for "Nested functions and closures" within that document.

Shrinath · Accepted Answer · 2011-09-12 05:22:38Z

0

It would alert "2".

Test your javascript examples here : jsfiddle.net

Your example is pasted here : your javascript example

And why the heck is var a unknown to n() ??

answered Sep 12, 2011 at 5:22

Shrinath

8,13813 gold badges51 silver badges86 bronze badges

Comments

RobG · Accepted Answer · 2011-09-12 06:30:59Z

0

a is decalred as a global variable and given a value of 1. a is also declared inside the function f() and given a value of 2. Function n() is declared inside the function f() and called after the assignment to the "inner" a.

So when n is called, the identifier a will be resolved from the scope of n. The first variable object on the scope chain with an a property is the one declared in f, so its value is returned.

edited Sep 12, 2011 at 6:30

RobG

148k32 gold badges180 silver badges216 bronze badges

answered Sep 12, 2011 at 5:21

Sai Kalyan Kumar Akshinthala

11.9k8 gold badges45 silver badges68 bronze badges

Collectives™ on Stack Overflow

Javascript function scope

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related