Javascript window.onload scope

Question

Can someone explain why the warning is returning "undefined" instead of "hello"?

window.onload = function() {  
    var a = 'hello';  
    alert(window.a);  
}

+2

teggy May 04 '10 at 1:02

2 answers

the variable 'a' is not part of the window in your context.

a is bound to the anonymous function you assigned to load.

you CAN add as a window member if you want:

window.onload = function() {  
    window.a = 'hello';  
    alert(window.a);  
}

but I suggest not to.

+5

Shawn dube May 4 '10 at 1:18

artlung · Accepted Answer · 2010-05-04T01:23:25+0000

"Named variables are defined using the var statement. When used inside a function, var defines variables with a scope function." - ( source )

To be globally accessible, and in particular to be a a

member of an object window

, modify your code as follows:

var a; // defined in the global scope
window.onload = function() {  
    a = 'hello'; // initialized
    alert(window.a);  
}

Or this way:

var b = 'world'; //defined and initialized in the global scope
window.onload = function() {  
    alert(window.b);  
}