Function scope in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of variable inside function scope

What will be the output of the following code?

Javascript

function test() {
  let message = "Hello";
  console.log(message);
}
test();
console.log(message);

A Hello\nReferenceError

B Hello\nundefined

C undefined\nHello

D ReferenceError\nHello

💡 Hint

Variables declared inside a function are not accessible outside it.

The variable 'message' is declared inside the function 'test', so it is only accessible there. The first console.log prints 'Hello'. The second console.log tries to access 'message' outside its scope, causing a ReferenceError.

❓ Predict Output

intermediate

Output of nested function accessing outer variable

What will this code print to the console?

Javascript

function outer() {
  let count = 5;
  function inner() {
    console.log(count);
  }
  inner();
}
outer();

A undefined

B 5

C ReferenceError

D 0

💡 Hint

Inner functions can access variables from their outer functions.

The inner function can see the variable 'count' declared in the outer function, so it prints 5.

❓ Predict Output

advanced

Effect of var in function scope

What is the output of this code?

Javascript

function example() {
  if (true) {
    var x = 10;
  }
  console.log(x);
}
example();

A 10

B ReferenceError

C undefined

D TypeError

💡 Hint

Variables declared with var are function-scoped, not block-scoped.

The variable 'x' declared with var inside the if block is accessible throughout the function, so console.log prints 10.

❓ Predict Output

advanced

Output with let inside block scope

What will this code output?

Javascript

function test() {
  if (true) {
    let y = 20;
  }
  console.log(y);
}
test();

A 20

B TypeError

C ReferenceError

D undefined

💡 Hint

Variables declared with let are block-scoped.

The variable 'y' is declared inside the if block with let, so it is not accessible outside that block, causing a ReferenceError.

❓ Predict Output

expert

Output of closures with loop and var

What will be the output of this code when calling all functions in the array?

Javascript

function createFunctions() {
  var funcs = [];
  for (var i = 0; i < 3; i++) {
    funcs.push(function() {
      return i;
    });
  }
  return funcs;
}
const functions = createFunctions();
const results = functions.map(f => f());
console.log(results);

A [0, 1, 2]

B [0, 0, 0]

C [undefined, undefined, undefined]

D [3, 3, 3]

💡 Hint

var is function-scoped and the loop variable is shared across all closures.

All functions share the same 'i' variable, which after the loop ends is 3. So each function returns 3.