If you're looking for JavaScript Interview Questions for Experienced or Freshers, you are at the right place. There are a lot of opportunities from many reputed companies in the world. According to research JavaScript has a market share of about 54.87%. So, You still have opportunity to move ahead in your career in JavaScript Development. Mindmajix offers Advanced JavaScript Interview Questions 2021 that helps you in cracking your interview & acquire a dream career as JavaScript Developer.

 JavaScript Interview Questions for Experienced, we will go through below topics

The Best JavaScript Interview Questions and Answers

Q1. What exactly do you know about JavaScript?

Ans: It is basically an object-oriented programming language that is having a lot of applications. It can be used for both server-side, as well as client-side scripting and the good thing is it is known to provide the best results in every aspect. When it comes to building HTML WebPages, this language is often considered and is known to bring the most desired outcomes.

Q2. On a client machine, how you will detect the server using JavaScript?

Ans: For this, task, the users can simply proceed with the navigator.app string. The string performs this task automatically and the user just needs to define it at the right time. Also, the users need to make sure that the instructions are executed in the right manner. Sometimes there is a need to define the IP or other address of the server that needs to be detected. 

Q3. What according to you is the true difference between Java and JavaScript?

Ans: Well, there are a few differences that separate both these terms from each other. Basically, JavaScript is a modified version or a coded version that is generally considered in the HTML pages while on the other side, Java is a well-known programming language used to develop applications in almost every category. Both these languages don’t depend on each other for their task and have separate applications. Generally, Java is considered as OOPS language while JavaScript is a scripting language preferred by the clients. Also, JavaScript has wide applications in HTML WebPages while Java is used mostly in developing computer applications. 

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Q4. If the argument is not a number, which function you will use in the JavaScript?

Ans: isNan function is useful in case the argument is not a number. Actually, it remains true if the argument doesn’t have a number while on the other side it remains false if it is.

JavaScript Interview Questions for 2 Years Experience

Q5. Compare ASP Script and JavaScript in terms of speed?

Ans: When it comes to speed, both of them are powerful but both have their own limits that put them separate from one another. JavaScript is known to have a quick speed for performing similar functions. This is because JavaScript doesn’t need the help of a web server to perform the task which is assigned to it. However, ASP is slow as compare to it. This is because of the very same reason and i.e. it depends largely on the webserver for executing the tasks assigned to it. Although the server-side version of JavaScript i.e. nodejs also exists, still it is known to provide quick results.

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Q6. How many data types are there in JavaScript? Can you name them?

Ans: There are 6 data types in JavaScript and they are:


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These data types are very useful and they have applications in almost every important task performed by JavaScript. 

Q7. How can you break the JavaScript code into different lines?

Ans: This can be done with the help of a backlash. However, you need to use it at the end of the initial line otherwise it will show an error at the end. The good thing is there is no limit on lines that can be created for the purpose of accommodating data. Also, doing this is not at all a big deal and one can easily handle this task.

Q8. Tell something about the undeclared and undefined variables?

Ans: Basically, there are a lot of programs that actually don’t exist in a program and are thus known as undeclared ones. There is always a runtime error displayed on the screen in case the program proceeds with reading the value of a variable that is not declared. On the other side, declared variables as the name indicates are those which are well defined within a program but haven’t been assigned any value by the operator. The value is always returned in case of the program proceeds with reading them.

Q9. Are you familiar with the concept of negative infinity in JavaScript?

Ans: Yes, it is actually a number present in this language and can simply be derived by dividing any number having a negative value with zero. There are basically some important applications of negative infinity in JavaScript. 

Q10. What exactly do you know about the global variables? Which keyword do you use to declare them?

Ans: There are variables in the language that generally doesn’t have much scope or their scope is limited. In JavaScript, Global variables are the same variables. To declare them, the keyword that can be used is var. the fact is most of the programmers avoid using this variable due to a major issue and i.e. the strong chances of clashing of variable names with the global, or with the local group. F course, it leads to many issues. In addition to this, there are certain chances of debugging issues that declare their presence with the global variables.

Q11. What are timers in JavaScript? What do you know about them?

Ans: There is a provision in JavaScript for the programmers to set a specific time when it comes to executing a code. This can be done with the help of timers. It is actually a similar phenomenon as we set an alarm on your cell phone. The code can also be repeated at a specific time once executed. There are functional such as setInterval, clear internal that can be considered for this. They make the coding simple and help programmers to boost their tasks simply. However, there is only one thread available and there are chances that events might be in a queue. Thus, sometimes users need to wait for the clearance of the same.

Q12. For single-line comment, which symbol you will use in the JavaScript?

Ans:      //
            The above symbol is used.

Q13. Are you familiar with the prompt box in JavaScript?

Ans:  Yes, basically many times a programmer has to enter the input values directly through the text box. The prompt box is something that is extremely helpful for the users during such a situation. Label and the box are provided for the ease of programmers. They are basically used for entering the number or the text simply. 

Q14. What exactly is the difference between Session State and the View State in JavaScript?

Ans: Session State is an option that can be considered to access all the pages within a web application while on the other side ViewState is used for accessing a session only

Q15. Is it possible in JavaScript to proceed with automatic type conversation?

Ans: Yes, it’s possible and there is nothing much programmers have to do to access it. It is actually the most common method used by the developers when it comes to conversion

Q16. Name the methods you can use to write and read a file with the help of JavaScript?

Ans: Through Active X objects and by using the JavaScript extensions it is possible to read and write the file in JavaScript.

Q17. What is a strict equality operator in JavaScript?

Ans: Many times during the code, there exists a problem or a condition in which more than one operand has similar values. The strict equality operator is capable to return the true value of the operand without interrupting the operation. 

Q18. Name the structures in v that can be considered as looping structures?

Ans: These are: While, For, and do-while loops

JavaScript Interview Questions for 5 Years Experience

Q19. In JavaScript, it is possible for the programmers to convert the string to an integer?

Ans: Yes, this can be done easily in JavaScript. For this, the function parseInt () is used. It generally takes the string into the first parameter and then to the next parameter which is considered as the base of given string. 

Q20. Name the two basic groups of data types in JavaScript?

Ans: These are:
         Reference types

Q21. In a program, how can you delete the variables? Is there any limit on deletion?

Ans: This task can be done simply with the help of an operator and i.e. Delete. Although it deletes all the variables, as well as the objects in a program but it’s is not possible for this operator to delete those objects and variables that are declared already with the VAR keyword. For deleting these variables, another command is to be followed. Any number of other variables can be deleted with this operator. It is also possible to erase a specific portion of a coding simply and without accessing any other command for this. 

Q22. When can you use NULL in JavaScript?

Ans: Basically, it is used when there is no object or there is no value is there on a string. It let the array proceed smoothly and perform its task very reliably. There is no need for the users to worry while executing this as it doesn’t show the runtime error in any stage. Also, this can be used in special cases to check whether all the strings have defined variables or numbers present with them or not. 

Q23. When can you have an error that says Undefined Value on the screen?

Ans: Well, if it appears, it simply means either the variable the user is considering doesn’t exist in the code. It is also possible that the property is not present. In addition to this, the error can also be due to the fact that variable hasn’t been assigned any value. Users need to make sure of these three steps before they proceed with anything. If this error is ignored, it can sometimes affect the entire code. 

Q24. How the button configuration in the Confirmation box is different from the Alert box in Javascript?

Ans: The basic difference is there are two buttons in the Conformation box and they are named OK and Cancel. On the other side, the Alert box contains only one button and i.e. OK. In addition to this, there are other differences in the configuration and they are hidden in a few cases for security purposes.

Q25. What exactly are the escape characters?

Ans: Many times the users have to work with the special characters for performing special functions. These are double quotes, single quotes, or sometimes ampersands. The Escape character is used in such a case. Users can make it display again anytime and this can be done with the help of a backlash. Backlash can simply be placed before the character and this makes them display in a proper manner.

Q26. In JavaScript, which method you will find similar to the pop method?

Ans: The Pop method is very much similar to the shift method but there are some noticeable differences. In the pop method, the last element of the defined array is taken generally and then the same is returned. This often cut down the size of the array. On the other side, Shift method generally considers the first element of the array or any other element in the beginning. 

Q27. What exactly are the JavaScript cookies?

Ans: These are basically the test files that have a smaller size and are generally stored in a workstation. They get created automatically when a user opens a webpage. This is for the information they need to store. This could be details of the username and the information related to what they are interested in. 

Q28. What exactly do you know about the variable typing in JavaScript?

Ans: It is basically an approach with the help of which it is possible for the developers to assign a number to any variable which can further be assigned to a string. It is also called a variable typing.

Q29. What issues can you face while using the innerHTML in JavaScript?

Ans: The very first problem that can be there is content replacement without any message. Appending approaches cannot be used and this is another drawback. There is no validation in the inner HTML and in many cases they need to be inserted in the document which causes errors on a large scale.

Q30. Can we consider JavaScript at the concept level, why or why not?

Ans: No, it cannot be considered at the Concept level. This is because the variables that are present in the function has a scope that is only limited inside the function. If they are approached outside the same, they are useless. Also, the functional defined have certain limits on them.

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