Question

1 – why when I run the below code I got undefind instead “a=1” ?

function f1(){a=1; f2();}
function f2(){return a;}
var a= 5;
a = f1();
​alert(a);​

like this example the resualt is “a=1”.

function f1(){a=1; f2();}
function f2(){alert(a);}
var a= 5;
f1();

Answer 1

With

a = f1();

you are assigning the result of calling f1 to a. Yet, f1 does not return anything, it evaluates to undefined. You’d need to use a return statement:

function f1(){a=1; return f2(); }

Btw, this is not a scope problem. You don’t have any variables that are local to your functions, everything accesses the same a.