Question

Consider the following JavaScript skeletal program:

// The main program
var x;
function sub1() {
var x;
function sub2() {
. . .
}
}
function sub3() {
. . .
}
Assume that the execution of this program is in the following unit order:
main calls sub1
sub1 calls sub2
sub2 calls sub3

a. Assuming static scoping, in the following, which declaration
of x is the correct one for a reference to x?
i. sub1
ii. sub2
iii. sub3
b. Repeat part a, but assume dynamic scoping.

Answer 1

The correct reference to variable x depends on the scoping method used: static or dynamic.

Step-by-step explanation:

In this JavaScript program, the variable x is declared at two different levels: at the global level in the main program, and at the local level in sub1.

a. Assuming static scoping, the correct reference to x would be the local declaration in sub1. This is because static scoping determines the scope of a variable based on its lexical nesting in the source code. In this case, sub1 is called before sub2, so the local declaration of x in sub1 is the correct reference.

b. Assuming dynamic scoping, the correct reference to x would be the global declaration in the main program. Dynamic scoping determines the scope of a variable based on the order of function calls at runtime. Since sub3 is called last in this execution order, it would look for x in sub2, then in sub1, and finally find it at the global level in the main program.