The Top 3 Interview JavaScript Questions 2023

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JavaScript Interview Questions<br>
JavaScript Interview Questions<br>

JavaScript, a cornerstone technology of the World Wide Web, is an essential skill for any web developer. In the landscape of job interviews for web development positions, certain JavaScript questions frequently arise. Understanding these questions and knowing how to approach them can significantly increase a candidate's chances of success. This article aims to shed light on the top three JavaScript interview questions, providing insights into what interviewers are looking for and how candidates can effectively respond.

1. Explain Event Delegation in JavaScript

Question: Event delegation is a common JavaScript pattern which interviewers ask about to assess a candidate's understanding of event handling and the Document Object Model (DOM).

Key Concepts:

  • Event Propagation: Understanding of event bubbling and capturing.
  • Benefits: Efficiency in handling events and memory management.
  • Use Cases: Suitable scenarios for implementing event delegation.

Sample Answer: Event delegation in JavaScript refers to the practice of attaching an event listener to a parent element rather than individual child elements. This approach leverages event bubbling, where an event triggered on a child element propagates up to parent elements. It’s efficient because it requires fewer event listeners, which is beneficial for performance and memory management. For instance, in a list with numerous items, instead of attaching an event listener to each item, one can attach a single listener to the list itself and use the event target to manage individual item events.

2. Describe the Difference Between var, let, and const

Question: This question tests a candidate's understanding of variable declarations and scope in JavaScript.

Key Concepts:

  • Scope: Global vs. block-level scope.
  • Hoisting: Behavior of variables when declared with var, let, or const.
  • Reassignment and Redeclaration: The rules governing the modification of variables.

Sample Answer: var declares a variable with function scope or global scope if declared outside a function. It is subject to hoisting, where the variable can be used before it’s declared. let and const are ES6 additions providing block-level scope, which is limited to the block, statement, or expression they are used in. let allows reassignment while const does not. Hoisting occurs with let and const too, but they remain in a “temporal dead zone” from the start of the block until the declaration is encountered, preventing access before declaration.

3. Explain Prototypal Inheritance

Question Overview: Understanding prototypal inheritance is crucial for JavaScript developers, as it’s a fundamental concept of how objects and functions interact in the language.

Key Concepts:

  • Prototype Chain: How objects inherit properties and methods.
  • Creating Objects: Use of constructor functions, Object.create(), or class syntax.
  • Performance: Implications of prototypal inheritance on memory and access time.

Sample Answer: Prototypal inheritance is a feature in JavaScript where objects inherit properties and methods from a prototype. Every JavaScript object has a prototype property, which is a reference to another object. When a property or method is accessed, JavaScript looks up the prototype chain until it finds it or reaches the end of the chain. This mechanism is more memory efficient compared to classical inheritance, as inherited properties are not copied in every object instance. Objects can be created using constructor functions, Object.create(), or the class syntax introduced in ES6, all utilizing prototypal inheritance.


Preparing for JavaScript interviews requires a solid understanding of core concepts, among which event delegation, variable declarations, and prototypal inheritance are crucial. Grasping these concepts not only helps in answering interview questions but also lays a strong foundation for effective JavaScript programming. Candidates are advised to combine theoretical knowledge with practical coding experience to demonstrate their proficiency convincingly.

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