JavaScript Functions Interview Questions

Question:

How are functions stored in memory by JavaScript? Here we have a function sum().

function sum(a, b) {
  return a + b;
}

How sum() function is stored in memory?

Answer:

JavaScript allocates a memory block, just like a memory is allocated for a variable. The definition of the function is then stored inside the variable. That is why if we print the value of sum in console, it prints out the full source code of the function.

console.log(sum);

Here is the console output:

Question:

Does a function always return a value?

Answer:

Yes. If there is a return statement, that value is returned. If there is no return statement, the function implicitly returns undefined.

Here is a function that explicitly returns a number.

function f() {
  return 7;
}
const result = f();
console.log(result); // 7

Here is a function that does not have return statement.

function f() {
  var a = 7;
}
const result = f();
console.log(result); // undefined