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So when I declare a variable outside the scope of any function, it becomes a property of the window object. But what about when I declare a variable inside the scope of a function? For example, in the following code I can treat x as a property of window, i.e., window.x, but what about y? Is it ever the property of an object?

var x = "asdf1";

function test() {
var y = "asdf2";
}

test();
zjmiller
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3 Answers3

4

It becomes a property of the Variable object associated with the function call. In practice, this is the same thing as the function call's Activation object.

I don't believe that the Variable object is accessible to running JavaScript code, though; it's more of an implementation detail than something you can take advantage of.

Access all local variables is a related question here on SO.

Community
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Ian Clelland
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  • +1 Though I think OP is wondering if it is accessible *as* a property of an object, so perhaps worth noting that the Variable object is not directly accessible. – user113716 Mar 01 '11 at 17:43
  • I believe it /is/ accessible via Function.__scope__ in SpiderMonkey up to (but not including) Firefox 4. No way to access it in any other UA, and nothing is guaranteed once you start screwing with that object in SpiderMonkey. – gsnedders Mar 02 '11 at 10:47
0

In order to declare a JS variable a property of an object you need to either use the new Object(); method or the {} syntax. 

var variableName = new Object();
var variableName = {myFirstProperty:1,myNextProperty:'hi',etc};

Then you can assign child objects or properties to said variable object

variableName.aPropertyNameIMadeUp = 'hello';
variableName.aChildObjectNameIMadeUp = new Object();

As such the new variable object is associated with a method if it is within the method call.

Cheers

a.stgeorge
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-1

See following example (I have copy from other question-answer) very nice: 

// a globally-scoped variable
var a=1;

// global scope
function one(){
    alert(a); 
}

// local scope
function two(a){
    alert(a);
}

// local scope again
function three(){
  var a = 3;
  alert(a);
}

// Intermediate: no such thing as block scope in javascript
function four(){
    if(true){
        var a=4;
    }

    alert(a); // alerts '4', not the global value of '1'
}


// Intermediate: object properties
function Five(){
    this.a = 5;
}


// Advanced: closure
var six = function(){
    var foo = 6;

    return function(){
        // javascript "closure" means I have access to foo in here, 
        // because it is defined in the function in which I was defined.
        alert(foo);
    }
}()


// Advanced: prototype-based scope resolution
function Seven(){
  this.a = 7;
}

// [object].prototype.property loses to [object].property in the scope chain
Seven.prototype.a = -1; // won't get reached, because 'a' is set in the constructor above.
Seven.prototype.b = 8; // Will get reached, even though 'b' is NOT set in the constructor.



// These will print 1-8
one();
two(2);
three();
four();
alert(new Five().a);
six();
alert(new Seven().a);
alert(new Seven().b);
Manish Trivedi
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    If you copied someone else's answer, you should at least provide a reference to it. Anyway, I don't think you've really answered the question. – user113716 Mar 01 '11 at 17:47
  • @patrick: I have copy this prog in my computer!! This is really good program for under-standing a object concept in java script – Manish Trivedi Mar 01 '11 at 17:52
  • i have go link. (search in google and find it) :) http://stackoverflow.com/questions/500431/javascript-variable-scope – Manish Trivedi Mar 01 '11 at 17:54