Preparing for a Javascript Developer role can be daunting, especially the interview phase. You might be asked a range of questions about your technical expertise, problem-solving skills and understanding of Javascript principles. To help you navigate your interview, we’ve compiled the top 10 questions typically asked with some example responses.
| Job Description | A JavaScript Developer is responsible for implementing the front-end logic that defines the behavior of the visual elements of a web application. They are also involved in connecting this with the services that reside on the back-end. They work alongside other team members to manage project timelines, deliverables, and resources. |
| Skills | Proficiency in JavaScript, Understanding of HTML5 and CSS3, Knowledge of JavaScript frameworks such as AngularJS, ReactJS, or Ember, Understanding of asynchronous request handling, partial page updates, and AJAX, Proficient understanding of cross-browser compatibility issues and ways to work around them, Familiarity with front-end build tools, such as Grunt and Gulp.js, Good understanding of browser rendering behavior and performance |
| Industry | Information Technology, Software Development, Web Development |
| Experience Level | Mid-Level |
| Education Requirements | Bachelor’s degree in Computer Science or related field |
| Work Environment | Office-based or Remote. Developers typically work in teams that use Agile methodologies. |
| Salary Range | $60,000 – $120,000 per year |
| Career Path | Junior Developer > Mid-Level Developer > Senior Developer > Team Lead > Software Development Manager |
| Popular Companies | Google, Facebook, Amazon, Microsoft, Netflix |
Javascript Interview Questions
Can you explain how ‘this’ keyword works in JavaScript?
How to Answer:
In your answer, it’s important to show that you have a deep understanding of the ‘this’ keyword and how it can behave differently depending on the context in which it’s used. Explain that ‘this’ generally refers to the object that a function is a method of, but its value can change depending on the context. Mention how ‘this’ behaves in global scope, inside a function, in an object method, in a constructor function, and when using call/apply/bind methods.
Example:
‘This’ keyword in JavaScript is a bit complex and its value depends on how a function is called. In a global scope, ‘this’ refers to the global object which is the ‘window’ in a browser. Inside a function, ‘this’ refers to the global object if the function is called in a non-method way, that is, not as an object method. However, if a function is called as an object method, ‘this’ refers to the object that the method is a part of. In a constructor function, ‘this’ refers to the newly created object. And when using call, apply, or bind methods, we can explicitly define what ‘this’ should refer to.
What is a closure in JavaScript and can you give an example?
How to Answer:
Begin by defining what a closure is in JavaScript. It is a function that has access to its own scope, the outer function’s scope, and the global scope. Then, give an example to illustrate. A well-explained code snippet will demonstrate your understanding effectively.
Example:
A closure in JavaScript is a function that has access to the function’s scope (which is created when the function is created), the outer function’s scope and the global scope. This allows the function to access variables from within these scopes. Here’s an example:
function outerFunc(outerVar) {
return function innerFunc(innerVar) {
console.log(‘outerVar:’, outerVar);
console.log(‘innerVar:’, innerVar);
}
}
const newFunc = outerFunc(‘outside’);
newFunc(‘inside’);
In this example, innerFunc is a closure that is able to access outerVar from its parent function outerFunc, in addition to its own innerVar.
Can you explain the difference between ‘==’ and ‘===’ in JavaScript?
How to Answer:
The candidate should explain that ‘==’ checks for equality in value, while ‘===’ checks for equality in both value and type. They should then provide an example to illustrate this difference.
Example:
‘==’ checks only for equality in value, not type. For instance, if we compare ‘5’ == 5 in JavaScript, it will return true because it’s only checking the values. However, ‘===’ checks for equality in both value and type. So, if we compare ‘5’ === 5, it will return false because ‘5’ is a string and 5 is a number, hence they are not of the same type.
How would you describe the event loop in JavaScript?
How to Answer:
You should start by explaining what an event loop is, detailing its role in the JavaScript runtime environment. You can then describe how the event loop works in a non-blocking way, by constantly checking the call stack to see if it’s empty, and if it is, taking the first event from the event queue and pushing it to the stack. It’s important to highlight that this mechanism allows JavaScript to be asynchronous and non-blocking.
Example:
The event loop is a mechanism in JavaScript that constantly checks if there is any task that needs to be executed. It’s one of the key components that makes JavaScript asynchronous and non-blocking. When JavaScript executes a script, it does so on a single thread. This means it can only do one thing at a time. However, thanks to the event loop, it can handle many tasks asynchronously. It does this by constantly checking if the call stack is empty. If it is, it takes the first task from the event queue and pushes it to the stack to be executed. This allows JavaScript to handle multiple simultaneous events without blocking the thread.
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