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JavaScript Object-Oriented JavaScript (2015) Introduction to Methods Finishing the Calculator

Irfan Hussain
PLUS
Irfan Hussain
Courses Plus Student 6,593 Points

What is State in JavaScript? Specially when working with objects.

What is State in JavaScript? Specially when working with objects.

Steven Parker
Steven Parker
229,921 Points

Do you have an example? The challenge you linked to doesn't seem to use it.

4 Answers

Thomas Nilsen
Thomas Nilsen
14,957 Points

Here is a small example for maintaining 'state' in javascript - through something called closures.

function count() {
    //Starting value
    var count = 1;

    return function() {
        //Since 'count' is not defined here
        //It goes up the scope-chain searching for it
        console.log(count++);
    }
}

var count = count();
count(); //outputs 1
count(); // 2
count(); // 3
Steven Parker
Steven Parker
229,921 Points

How does this example represent "State"?

Thomas Nilsen
Thomas Nilsen
14,957 Points

What I did in my example was:

Setting a closure scope and return a function that has access to that scope. Every time that function is called, the state will remain as long as that function exists.

Here is a slightly different example with objects, men the idea is still the same. (This one is from StackOverflow):

var myStatefulObj = function() {

    // set up closure scope
    var state = 1;

    // return object with methods to manipulate closure scope
    return {
        incr: function() {
            state ++;
        }, 
        decr: function() {
            state--;
        },
        get: function() {
            return state;
        }
    };

}();

myStatefulObj.incr();
var currState = myStatefulObj.get();  // currState === 2
myStatefulObj.decr();
currState = myStatefulObj.get();  // currState === 1
Steven Parker
Steven Parker
229,921 Points

So you're naming the value you get from the internal variable "count" as "currState". But the name is arbitrary. If the closure contained 3 variables instead of just 1, what would you call the other 2?

This is, however, a good example of "scope".

Thomas Nilsen
Thomas Nilsen
14,957 Points

yeah - I agree the naming in my last example was bad (updated it now).

I'm not sure I understand what you mean "...If the closure contained 3 variables instead of just 1, what would you call the other 2"?

Steven Parker
Steven Parker
229,921 Points

I can be more specific when you give an example, but just in general "State" has no special meaning in JavaScript.

You probably saw it used with some code that is written to use it as a variable or passed argument to represent something.