JavaScript Functions - Practice Questions 2026 - Free Online Course

Mastering JavaScript functions is the single most important step in becoming a proficient web developer. Whether you are preparing for technical interviews, coding bootcamps, or complex project development, understanding how functions behave is critical. These practice exams are designed to move you beyond syntax and into a deep, logical understanding of JavaScript execution.

Why Serious Learners Choose These Practice Exams

Serious learners understand that watching tutorials is not enough. To truly internalize concepts like closures, hoisting, and the 'this' keyword, you must test your knowledge against challenging, unpredictable scenarios. This course offers:

Deep Conceptual Clarity: We don't just ask what code does; we explain why it happens based on the ECMAScript engine logic.
Active Recall Training: By working through a massive bank of original questions, you strengthen your ability to debug code mentally.
Risk-Free Learning: With a 30-day money-back guarantee and mobile compatibility, you can study anywhere, anytime, with total peace of mind.

Course Structure

The curriculum is divided into six logical stages to ensure a smooth learning curve from beginner to expert levels.

Basics / Foundations: This section covers the fundamental syntax of function declarations and expressions. You will practice identifying parameters versus arguments and understanding the basic return behavior of functions.
Core Concepts: Here, we dive into scope and the difference between global and local execution contexts. You will tackle questions regarding function hoisting and how the JavaScript engine initializes functions during the creation phase.
Intermediate Concepts: This module focuses on Arrow Functions, the "arguments" object, and Rest/Spread operators. You will learn the nuances of lexical scoping and how arrow functions differ from traditional functions in their handling of context.
Advanced Concepts: Prepare for the "tricky" parts of JavaScript. This includes deep dives into Closures, Higher-Order Functions (HOFs), Recursion, and the explicit binding of 'this' using Call, Apply, and Bind.
Real-world Scenarios: Practice solving problems that mimic actual development tasks. This includes debouncing/throttling concepts, callback patterns, and handling asynchronous function execution.
Mixed Revision / Final Test: A comprehensive evaluation that pulls from all previous sections. This final exam is designed to simulate the pressure of a real technical interview.

Sample Practice Questions

Question 1

What is the output of the following code?

JavaScript

const result = (function(a) {

delete a;

return a;

})(10);

console. log(result);

Option 1: undefined
Option 2: null
Option 3: 10
Option 4: ReferenceError
Option 5: NaN

CORRECT ANSWER: Option 3

CORRECT ANSWER EXPLANATION: The 'delete' operator is used to remove properties from objects. It has no effect on local variables or function parameters. In this Immediately Invoked Function Expression (IIFE), 'a' is a parameter. Therefore, 'delete a' does nothing, and the function returns the original value passed to it, which is 10.

WRONG ANSWERS EXPLANATION:

Option 1: Incorrect because 'a' was never deleted; it still holds the value 10.
Option 2: Incorrect because JavaScript does not automatically assign 'null' unless explicitly defined.
Option 4: Incorrect because 'a' is still defined within the function scope.
Option 5: Incorrect because no mathematical operations resulted in an invalid number.

Question 2

Consider the following code:

JavaScript

var x = 21;

var girl = function () {

console. log(x);

var x = 20;

};

girl();

Option 1: 21
Option 2: 20
Option 3: ReferenceError
Option 4: undefined
Option 5: null

CORRECT ANSWER: Option 4

CORRECT ANSWER EXPLANATION: This is a classic example of hoisting. Inside the 'girl' function, the declaration 'var x' is hoisted to the top of the local scope. However, the initialization (x = 20) remains at the bottom. Therefore, when 'console. log(x)' is called, the local 'x' exists but hasn't been assigned a value yet, resulting in 'undefined'.

WRONG ANSWERS EXPLANATION:

Option 1: Incorrect because the local declaration of 'x' shadows the global 'x'.
Option 2: Incorrect because the assignment happens after the console log.
Option 3: Incorrect because 'var' declarations do not throw ReferenceErrors when accessed before initialization (unlike 'let' and 'const').
Option 5: Incorrect because 'null' is an intentional assignment, not a default state for hoisted variables.

Welcome to the best practice exams to help you prepare for your JavaScript Functions. Our goal is to ensure you feel confident in any coding environment.