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

Assuming static scoping, in the following, which declaration of x is the correct one for a reference to x ?

A) sub1
B) sub2
C) sub3

Answer 1

In JavaScript's static scoping, references to a variable x in sub2 would use the declaration within sub1. However, for references in sub3, which is not nested within sub1, they would default to the global scope's x declaration.

Step-by-step explanation:

Understanding the scoping rules in programming is crucial for determining which variables are accessible in different parts of the code. In JavaScript, static or lexical scoping determines the scope of a variable at the time the function is defined, not when it is executed. In the given skeletal program structure, a variable x is declared in both the main program and within the function sub1. No declaration of x exists in sub2 and sub3.

When considering static scoping, if a variable is referenced within a function, the interpreter looks up for the variable definition starting from the current function's scope and moves outwards if it's not found. Since sub2 is nested within sub1, and sub1 has its own declaration of x, references to x within sub2 would correspond to the declaration within sub1. Even though sub2 calls sub3, sub3 would not know about the x defined in sub1 because it is out of scope. So, for a reference to x within sub3, it would use the x declared in the main program.

Therefore, the correct answer for the declaration of x that would be used for a reference to x within sub3 would be A) sub1 for references in sub2 and the global scope's x for references in sub3.