Question

I am learning javascript and can someone please explain the following code snippet for me?

var state=true;
function bob(){ var state=false; }
bob() 

What should be the state value and why?

Many thanks,
L

Answer 1

At the end of execution, state will be true, because the function bob() defines a local variable named state instead of assigning to the global variable of the same name. However, in the following example, state would be false:

var state=true;
function bob(){ state=false; }
bob();

By omitting the var keyword, the JavaScript engine will travel up the scope chain looking for a variable named state, until it finds one or reaches the global scope. This can be further demonstrated with nested functions:

var state = true; // global
function bob() {
    var state = true; // local to `bob()` 
    function jim() {
        state = false;
    }
    jim();
    alert(state); //-> false, `jim()` modifies `bob()`'s variable
}
bob();
alert(state); //-> true, `jim()` and `bob()` don't touch the global variable