What hoisting is in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code involving hoisting?

Consider this JavaScript code snippet. What will it print to the console?

Javascript

console.log(a);
var a = 5;

A undefined

B 5

C ReferenceError

D null

💡 Hint

Think about how variable declarations are handled before code runs.

In JavaScript, variable declarations with var are hoisted to the top, but their assignments are not. So 'a' is declared but undefined at the time of console.log.

❓ Predict Output

intermediate

What will this function print due to hoisting?

Look at this code. What is the output when calling foo()?

Javascript

function foo() {
  console.log(bar);
  var bar = 'hello';
}
foo();

A hello

B ReferenceError

C undefined

D null

💡 Hint

Remember that variable declarations are hoisted but assignments are not.

Inside the function, 'bar' is declared but not assigned before console.log, so it prints undefined.

❓ Predict Output

advanced

What is the output of this code with let and hoisting?

What will this code print to the console?

Javascript

console.log(x);
let x = 10;

A ReferenceError

B undefined

C null

D 10

💡 Hint

Variables declared with let are not hoisted like var.

Variables declared with let are in a temporal dead zone before initialization, causing a ReferenceError if accessed early.

❓ Predict Output

advanced

What will this code output with function hoisting?

What does this code print when run?

Javascript

foo();
function foo() {
  console.log('Hi');
}

A ReferenceError

B undefined

C TypeError

D Hi

💡 Hint

Function declarations are hoisted completely.

Function declarations are hoisted with their body, so foo() can be called before its definition.

❓ Predict Output

expert

What is the output of this tricky hoisting example?

What will this code print to the console?

Javascript

console.log(typeof foo);
var foo = 'bar';
function foo() {}

A string

B function

C undefined

D ReferenceError

💡 Hint

Function declarations are hoisted before variable declarations.

Function declarations are hoisted before var declarations, so typeof foo is 'function' at the time of console.log.