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Javascript Interview Questions

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  1. What are some of the primary differences between monolithic and microservice architectures, and which is a better option for flexibility and scalability? See answer
  2. What is the difference between synchronous and asynchronous programming, and how does asynchronous programming relate to your work with JavaScript? See answer
  3. Do you have a preference between class inheritance and prototypal inheritance in JavaScript? If so, why? See answer
  4. In your opinion, is classical inheritance ever the right choice? If so, when? If not, why? See answer
  5. How would you define functional programming? What is the role of functional programming in JavaScript? See answer
  6. What are the benefits of using functional programming methods instead of object-oriented programming? Can you provide an example? See answer
  7. How would you define one-way data flow and two-way data binding? What is the difference between the two? See answer
  8. Why are Boolean terms important in JavaScript? See answer
  9. Are you willing to learn new programming languages compatible with JavaScript to complete company goals?
  10. Explain the five main types of data used in JavaScript and when to use each one.
  11. Provide an example of when it would make sense to code a timer when programming with JavaScript.
  12. What strategies do you use to provide consistent documentation when making updates to someone else’s original JavaScript code?
  13. What steps would you take if you couldn’t figure out why the code you wrote wasn’t functioning properly?
  14. Have you ever built a clicker counter from scratch before?
  15. What is the purpose of a deferred script and what is an example of the code you would use to implement them?
  16. What kinds of errors do you see in JavaScript and how do you troubleshoot each one?
  17. Do you have experience writing custom code based on-screen object feedback?
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8 Javascript Interview Questions and Answers

Q:

What are some of the primary differences between monolithic and microservice architectures, and which is a better option for flexibility and scalability?

A:

This question is helpful in assessing foundational coding knowledge. There are several possible answers, so listen for thorough responses that demonstrate an understanding of monolithic versus microservice architectures.
What to look for:

  • The applicant’s familiarity with coding
  • The applicant’s understanding of the pros and cons of different approaches to architecture
  • An ability to articulate how to transition from monolithic to microservice

Example:

“Designing a monolithic architecture is less expensive in the short term, but the code is a single cohesive unit that shares resources and memory space. Microservice architecture offers flexibility and scalability, because each component is an independent application.”

Q:

What is the difference between synchronous and asynchronous programming, and how does asynchronous programming relate to your work with JavaScript?

A:

Asynchronous programming permits multiple concurrent operations, and it is a good match for JavaScript programs. This question assesses general coding knowledge, as well as specific understanding of JavaScript.
What to look for:

  • An ability to articulate the difference between synchronous and asynchronous programming
  • The impact of asynchronous programming on user interfaces
  • An understanding of blocking and the subsequent impact on performance

Example:

“In simple terms, synchronous programming means the code is executed in a linear fashion. These programs cannot typically handle simultaneous operations. With asynchronous programming, there is an event loop. As a result, one program thread can handle multiple operations at the same time. Since JavaScript is often used in user interfaces, the ability to run multiple operations concurrently results in a better user experience.”

Q:

Do you have a preference between class inheritance and prototypal inheritance in JavaScript? If so, why?

A:

This question is helpful in learning whether the applicant has experience and expertise in JavaScript. Prototypal inheritance is easier and more flexible than classical inheritance, which makes it the preferred method for experienced JavaScript coders.
What to look for:

  • A preference for prototypal inheritance and composition
  • An ability to articulate the reasons for this preference
  • References to functional inheritance, concatenative inheritance, prototype delegation and object composition

Example:

“When using class inheritance, instances inherit from classes. This creates hierarchical class taxonomies. On the other hand, with prototypal inheritance, instances inherit from other objects, and they can be created from multiple objects. I prefer prototypal inheritance, because it is easier and more flexible.”

Q:

In your opinion, is classical inheritance ever the right choice? If so, when? If not, why?

A:

How applicants answer this question gives you insight into their experience with JavaScript. There are very few instances when classical inheritance makes sense, and the applicant might say there are none at all. A “no” answer is preferable to a long list of appropriate circumstances, as these are typically based on misinformation.
What to look for:

  • Classical inheritance is never or almost never the right choice
  • Applicants’ ability to articulate reasons for their responses
  • Applicants’ ability to defend their reasoning with logic

Example:

“Classical inheritance is almost never the right solution. On very rare occasions, it might be used for a single level.”

Q:

How would you define functional programming? What is the role of functional programming in JavaScript?

A:

Functional programming is a fundamental principle in current JavaScript use. Applicants’ ability to answer this question fully gives you assurance of their foundational knowledge.
What to look for:

  • Mention of function purity and side effect avoidance
  • Ability to provide examples of functional programming languages
  • Ability to identify the features of JavaScript that enable functional programming

Example:

“Functional programming permits the design of software through the use of pure functions. This method avoids programming issues such as shared state, side effects and mutable data. It is used as an alternative to object-oriented programming, in which the application state is typically collocated and shared with methods in objects.”

Q:

What are the benefits of using functional programming methods instead of object-oriented programming? Can you provide an example?

A:

Any applicant with JavaScript experience has used one of these styles and therefore should be able to offer some thoughts on the pros and cons of each. This question assists you in measuring the depth of the applicant’s experience with JavaScript.
What to look for:

  • An ability to articulate advantages and disadvantages of either method
  • Mention of the issues that result from shared resources
  • An understanding of how functional programming simplifies applications

Example:

“While I have primarily worked with object-oriented programming, I am looking forward to developing functional programming skills. I have had trouble with object-oriented programming, because different components are competing for the same resources.”

Q:

How would you define one-way data flow and two-way data binding? What is the difference between the two?

A:

The applicant’s ability to answer this question demonstrates deep understanding of the important foundational principles of JavaScript. Candidates who are unfamiliar with these terms may not have the experience required to be successful in the position.
What to look for:

  • Ability to define the two concepts in a clear, concise manner
  • Ability to articulate the difference between the two concepts
  • Mention of example frameworks

Example:

“One-way data flow occurs when the model is the single source of truth. React is an example of this. Alternatively, two-way data binding is a state in which user interface fields are dynamically linked with model data. When a field in the user interface changes, the model changes, too. Angular is an example of this.”

Q:

Why are Boolean terms important in JavaScript?

A:

Boolean logic is an essential part of JavaScript infrastructure and governs how programmers write code. It guides the structure of JavaScript and explains the rules that keep code consistent. Anyone who uses JavaScript in their role should have a strong understanding of the theory and logic behind the code they write. This question helps the interviewer identify the comprehension level of each applicant and select candidates who have a strong understanding of both the JavaScript framework and its potential applications.

A good answer will include:

  • Definition of Boolean
  • Example of Boolean terms
  • Understanding of how Boolean operations influence their work

Here's an example of a great answer:

Example:

"Boolean terms are essential in determining how clients can interact with a webpage and what results they will get for different actions. Boolean terms indicate which values elicit different responses from the page. They also show other coders what logic I used to program the page so they can make appropriate adjustments. For example, the coding phrase 'if (age > 21)' could direct people over 21 to a restricted webpage while directing people under 21 to an error message."

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