Essential Prescreening Questions to Ask When Hiring a Senior Javascript Developer: A Comprehensive Guide

What frameworks of JavaScript do you consider yourself an expert in?

A candidate's answer to this question will help you identify their strengths and weaknesses. Each framework, such as React, Angular, or Vue, has its own unique set of features and best practices. An expert in a specific framework will have a deep understanding of its architecture and will be able to leverage its features to create robust, scalable applications.

How do you handle asynchronous operations in JavaScript?

This question is designed to test the candidate's understanding of asynchronous programming in JavaScript. Their answer should cover concepts like callbacks, promises, async/await, and how they can be used to manage asynchronous operations.

Can you explain closures in JavaScript and provide an example of how you have used them in your projects?

Closures are a fundamental aspect of JavaScript programming. A solid understanding of closures and how to use them effectively is a good indicator of a developer's proficiency in JavaScript. The candidate should be able to explain what a closure is, why it is useful, and provide a practical example from their previous work.

What is your experience with JavaScript testing frameworks?

Testing is an integral part of software development. It ensures the code is working as expected and helps prevent bugs from making it into the final product. The candidate should be familiar with at least one JavaScript testing framework, such as Jest or Mocha, and be able to discuss their experience using it in a project setting.

Can you explain how 'this' keyword works in JavaScript?

The 'this' keyword is a complex yet crucial part of JavaScript. Understanding how it works and when to use it is a sign of a seasoned JavaScript developer. The candidate should be able to explain the different contexts where 'this' changes its value and how to handle those situations.

What strategies do you use to debug JavaScript code?

Debugging is an inevitable part of programming. A good developer should have a set of strategies to quickly identify and resolve issues in their code. The candidate should be able to discuss their debugging process, mention any tools they use, and give examples of how they've solved difficult bugs in the past.

How do you ensure your JavaScript code is secure?

Security is a critical concern in web development. The candidate should be able to explain how they write secure JavaScript code, including practices such as input validation, output encoding, and proper error handling.

What are some performance considerations for JavaScript?

Performance is a key factor in user experience. The candidate should understand how JavaScript performance can impact a web application and discuss strategies to optimize it, such as minimizing DOM manipulation, leveraging browser caching, and using efficient algorithms.

How do you manage state in a JavaScript application?

State management is a key concept in modern JavaScript applications. The candidate should be able to explain how they manage state, including the use of libraries or frameworks such as Redux or Vuex.

What are some of the ES6 features you have used in your projects?

ES6, or ECMAScript 2015, introduced several new features to JavaScript, such as arrow functions, template literals, and destructuring assignments. The candidate's familiarity with these features can help you gauge their up-to-date knowledge of the language.

Can you describe how prototypal inheritance works in JavaScript?

Prototypal inheritance is a core concept in JavaScript. The candidate's understanding of this concept can be a good indicator of their overall JavaScript proficiency. They should be able to explain how objects can inherit properties from other objects, and how this differs from classical inheritance.

What is your experience with build tools and task runners like Webpack, Grunt or Gulp?

Build tools and task runners are essential in modern JavaScript development. They automate tasks such as bundling and minifying code, compiling Sass or Less to CSS, and refreshing the browser automatically when files change. The candidate's experience with these tools can give you an idea of their familiarity with modern development workflows.

What is your experience with JavaScript-based mobile app development?

With the rise of frameworks like React Native and Ionic, JavaScript has become a popular choice for mobile app development. If your project involves building a mobile app, it's crucial to find a developer who has experience in this area.

What is your experience with server-side JavaScript development, such as Node.js?

Server-side JavaScript development, particularly using Node.js, is a valuable skill for modern web developers. The candidate's experience with this can give you an insight into their ability to handle full-stack development and work with back-end technologies.

How do you handle error handling and exceptions in JavaScript?

Error handling is a critical aspect of any programming language. The candidate should be able to explain their strategies for catching and handling errors and exceptions in JavaScript, which can help prevent crashes and improve the user experience.

What is the difference between null and undefined in JavaScript?

This question is a common one in JavaScript interviews and tests the candidate's understanding of the language's nuances. The candidate should be able to explain the differences between null and undefined, and when each is typically used.

What is event bubbling and capturing in JavaScript?

Event bubbling and capturing are two ways of event propagation in the HTML DOM API. The candidate's understanding of these concepts can be an indicator of their proficiency in handling user interactions and DOM manipulation.

What are JavaScript Promises and how have you used them in your projects?

JavaScript Promises are a way of handling asynchronous operations. The candidate's familiarity with Promises and their usage can give you an idea of their ability to handle complex, asynchronous tasks in JavaScript.

Can you explain how the map() function works in JavaScript?

The map() function is a higher-order function that is frequently used in JavaScript. The candidate's understanding of how it works and its usage can provide insight into their knowledge of JavaScript's functional programming aspects.

What is your experience with TypeScript or any statically typed superset of JavaScript?

With the increasing popularity of TypeScript and other statically typed supersets of JavaScript, having experience with these technologies is a valuable asset. The candidate's experience with TypeScript or similar technologies can give you an idea of their ability to work in a type-safe environment and their understanding of type systems.