15 JavaScript Interview Questions and Answers You should Know

JavaScript is a popular programming language to build highly engaging websites and apps. It is used by close to 65% of developers, according to Stack Overflow 2021 survey. Most of our prescreened developers at Reintech also rely on the language to woo clients.

Therefore, businesses are always in search of top JavaScript talents to gain a competitive edge. JavaScript developers are also pleased, as they get attractive remuneration and a chance to grow their careers.

However, every JavaScript programmer needs to sit for an interview to get selected. Employers should also utilize the opportunity to assess the skills and capabilities of the developer.

15 JavaScript Interview Questions

Here are some of the best JavaScript interview questions (with answers) to ask when you hire JavaScript developers.

1. What do you mean by event delegation?

Event delegation allows us to handle events with convenience. It eliminates the need for adding event listeners to every event that is of similar nature. Developers can add event listeners to a parent event instead and rely on the .target property of an event object. It will allow us to call an event on a specific target.
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2. What is the use of ECMAScript?

ECMAScript is a standard that puts forward the rules and conditions for any scripting language to be ECMAScript compliant. JavaScript is a scripting language that follows the guidelines of ECMAScript. The standard aims to create interoperability between scripting languages using the rules.

3. When should you use prototypal inheritance?

Prototypal inheritance is a suitable choice where we cannot use functional programming or modules. They allow composition that creates can-do, uses-a, or has-a relations instead of is-a relation developed with class inheritance. Additionally, different types of prototypal inheritance are used for different use cases.

4. What is the use of strict mode in JavaScript?

The strict mode in JavaScript enables programmers to compile secure code. It brings up more exceptions and helps in the identification of hidden bugs. Additionally, strict code may run faster compared to regular code in some situations. Moreover, it helps developers deactivate features that are not well-planned or lack quality.
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5. How can you delete a cookie with JavaScript?

You can delete a cookie in JavaScript by changing the expiration date to one in the past. The process will force the cookie to not return any result if someone tries reading it. In some browsers, it is necessary to define your cookie path to delete it.

6. What is the difference between one-way data flow and two-way data binding?

One-way data flow allows data to move in one direction and makes it easy to comprehend. It also signifies the model is a single source of truth. Additionally, only the model is granted access to manipulate the state of the app.

Two-way data binding indicates the model and data are dynamically bounded. So, any change in model data or UI field affects the other one.

7. What do you mean by higher-order function? Can you give some examples?

A higher-order function returns a chosen function as a return value. Else, it can also accept another function as an argument. Sometimes both are possible. Examples of built-in higher-order functions in JavaScript are reduced, filter, and map.

8. What are the two types of typed language?

The two types of typed language are dynamically and statically typed language. Dynamically typed language can accommodate numerous types. On the other hand, statically typed language can accommodate only one type. In both cases, values relate to values instead of variables.
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9. What are the benefits of microservice architectures?

Microservices allows an app to run based on several individual applications. It is easy to maintain such architectures as the components are not dependent on one another. Additionally, microservices make your app easier to arrange. We can also make changes to the code easily without affecting the whole app.

10. What is the use of the prompt box?

A prompt box in JavaScript provides the user a text box to type in an input. Developers may display a dialogue in the prompt box and ask the user to click any button like “Accept” or “Cancel.” The user can proceed to the website or page only after providing the input.

11. What are the different types of error name values in JavaScript?

JavaScript comes with six error name values. They are URI error, type error, syntax error, reference error, range error, and eval error.
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12. How can you embed JavaScript code in HTML files?

We can use several ways to embed JavaScript code in HTML files. One way is to embed them as functions and statements within a