Top 10 JavaScript Interview Questions

Picture this, you have all these dreams and aspirations to become a programmer, so you walk into an interview and you feel like you have all your basis covered. The interviewer sits you down and begins asking you questions related to various topics related to the field of Computer Science. You answer to the best of your abilities. The interviewer changes tactics and begins asking about programming in general, with JavaScript being the major contender.

What kind of questions would be good enough to test your knowledge of JavaScript programming?

In situations like that, it is best to know the basics of coding, for sure. But you must also be prepared for any outliers or left-field questions. JavaScript has become universal in the sense that all major platforms make use of it.

With the increase in advanced web applications, there has been a need for faster processing speeds and higher performance functionality. The reason for which web developers tend to gravitate towards programming languages that can help them render the best results which are in conjunction with the public demand.

Its functionality in different spectrums of website development and software is unparalleled. Some of the most used open-source libraries are part of the JavaScript modules, such as Angular, Vue.js, Node.js, and Aurelia—to name a few. All of these apply in various fields of either web development, or in IoT applications.

Basically, when it comes to scalability, functionality, and usability, JavaScript is leagues ahead of other programming languages.

Keeping that in mind, here are the top 10 questions that most interviewers go for to test your knowledge about JavaScript:

Question # 1: Is JavaScript case-sensitive?
Answer:

Yes, JavaScript is case-sensitive and all identifiers for variables, constants, keywords, functions, etc., must be typed carefully.

Question # 2: Name 5 of the most used JavaScript libraries?
Answer:

1. jQuery Library

2. React Library

3. Angular.JS

4. Vue.JS

5. Node.JS

Question # 3: What is callback function?
Answer:

A callback function is a JavaScript function that prompts an argument to be executed after the other function finishes execution.

Question # 4: What is closure?
Answer:

Closure is a function created whenever a variable is defined outside the scope from some inner scope, simply said, it defines a function from within another function and brings it to the forefront.

Question # 5: Major difference between Java and JavaScript?
Answer:

Java is an object-oriented programming language that runs its code on a virtual machine or browser, while JavaScript is an object-oriented scripting language that works only on a browser.

Question # 6: What are the ways to define variables in JavaScript?
Answer:

1. Var – to declare a variable

2. Const – a function declared as a constant

3. Let – a signal to indicate a variable might be reassigned

    Question # 7: What are the advantages of using JavaScript?
    Answer:

    1. Fewer server interactions

    2. Immediate response/feedback rate

    3. Better Interfaces

    4. Increased Interactivity

    Question # 8: What is NaN?
    Answer:

    NaN is an acronym for Not a Number, which occurs when a script or string is being converted into a number and it can not happen, thus giving NaN.

    Question # 9: Define Attributes and Properties?
    Answer:

    Attributes – gives more details on elements like value, id, etc.

    Properties – value assigned to property type.

    Question # 10: What is the difference between ‘==’ and ‘===’?
    Answer:

    The ‘==’ operator does type conversion of operands before comparison, and the ‘===’ operator compares the values as well as the data types of the operands.

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