Top 30 JavaScript Questions With Answers

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JavaScript is one of the most powerful and flexible programming languages that is employed consistently by different web browsers. This language is considered a core component of web technology along with HTML and CSS.  While CSS is responsible for style and HTML for structure, JavaScript offers interactivity to pages in the web browser.

As per Stack Overflow’s Annual Survey of 2018, for the sixth year in a row, JavaScript has been found to be the most commonly used programming language. The survey also found that JavaScript-based technologies like React, Node.js, and AngularJS topped the list of the most commonly used tools, libraries, and frameworks.  According to Web3Techs (Web Technology Surveys) reports, 95% of websites use JavaScript and the language also ranks the highest as the most popular client-side languages. As you can see, the popularity of JavaScript is indisputable. One of the main reasons for this is due to the ubiquity of web browsers.

This popularity has inadvertently led to an increased demand for Java professionals. If you are a fresher or an experienced professional looking to tap into the potential of this lucrative domain, this article will assist you in that. In this article, we have compiled the most frequently asked JavaScript questions, which will help you to land your dream career as a JavaScript professional.

1. What do you know about JavaScript?

JavaScript is essentially an object-oriented programming language which has many applications. This language can be utilized for both client and server- side scripting. Whichever way it is employed, it gives the best search results in all ways. JavaScript is the best programming language to build HTML web pages.

  1. Using JavaScript, how can you find out the server on a client’s computer?

You can use navigator.app string for this task. The string will automatically carry out this task and you should take care to define it at the correct time. The user should also ensure that the instructions are performed in the correct way. There might be instances where some other address of the server or IP needs to be defined in order to find it.

  1. What is the difference between Java and JavaScript explain?

JavaScript is basically a modified version that is usually employed in the HTML pages whereas the programming language Java is widely used for building apps in nearly every category. These programming languages function on their own and do not rely on one another for any of their tasks and have separate applications as well. While Java is an object-oriented programming language, JavaScript is a scripting language of choice to the clients. Additionally, Java is mostly used to develop computer applications and JavaScript has an array of applications in HTML web pages.

  1. Which function will you use in JavaScript when the argument is not a number?

If the argument is not a number, isNaN function can be used. This function yields true if the argument is not a number and false otherwise.

  1. In terms of speed, which is better: JavaScript or ASP Script?

Both JavaScript and ASP Script are powerful when it comes to their quickness, though each has its own limitations which sets them distinct from each other. JavaScript is quicker for carrying out similar functions because it does not require a web server for executing the assigned task. ASP Script is slower because for the most part, it depends on web servers for performing the tasks given to it. Though Node. js, the server side of JavaScript exists, it still provides fast results.  

  1. What are the data types in JavaScript?

JavaScript has 6 data types, They are:

  • String\
  • Object
  • Function
  • Number
  • Undefined
  • Boolean

The above-mentioned data types are highly beneficial and have applications in nearly every crucial function performed by JavaScript.

  1. How is it possible to break JavaScript code into various lines?

JavaScript code can be broken into different lines by using a backlash. You should take care that you use it at the end of the first line, or else it will be displayed as an error at the end. One good feature is that there is no cap on the number of lines that can be developed for accommodating data. This task can also be performed easily.  

  1. What are undefined and undeclared variables?

There are many programs that actually does not exist in a program. These are referred to as undeclared variables. A runtime error is shown on the screen if the program goes on to read the value of the undeclared variable. Whereas declared variables are those that are defined properly within a program, but have not been given any value by the user. In case the program goes further with reading them, the value is always returned.

  1. What is negative infinity in Javascript?

Negative infinity is a number that is there in JavaScript which can be basically derived by dividing any number with negative value with zero. In JavaScript, there are a few important application of negative infinity.  

  1. What do you understand about the term Global variables and mention which keyword is used for declaring them?

In programming languages, there are certain variables with very limited scope or no scope at all. In Javascript, these variables are known as Global variables. Var is the keyword used to declare this kind of variables.  Most programmers do not use this type of variables as there is a possibility of clashing the variable names with the local group or global. Moreover, there might also be a certain debugging issue that might arise with global variables.

  1. What are timers in javascript? Explain what you understand about the term

In the programming language JavaScript, there is a way for programmers to set a particular time for performing a code. This is accomplished by Timers. Timers are actually like the alarm clock on your phone. Once executed, it is possible to repeat the code at a particular time. Functions such as clearInterval and setInterval can be used for this. These functions make coding easier and enable programmers to perform their tasks effectively. Having said this, there is a single available thread and there is a chance that the events might be in a queue. Thus, the users might sometimes be required to wait for its clearance.

  1. Which symbol will you use in JavaScript for single line comment?

In JavaScript, the symbol // is utilized for single line comment.

  1. What is a prompt box in JavaScript?

A lot of times, programmers are required to use the text box to directly enter the input values. In such instances, a prompt box is of great help to the users.  Box and label are available for making it easy for programmers and to simply enter the text or the number.

  1. What is the difference between ViewState and session state in Javascript?

While View State is used only for accessing a session, Session State is a function that is used for accessing all pages within a web application.

  1. Can you go forward with automatic type conversion in JavaScript?

Yes, it is possible to access it very easily. Automatic type conversion is actually a basic method type that most developers employ for conversion.

  1. In JavaScript, what are the methods that can be used for reading and writing a file?

You can use JavaScript extensions and Active X for reading and writing the file in JavaScript.

  1.  In JavaScript, what is strict equality, operator ?

There are many instances while writing a code that the user finds that more than one operator might have the same values. This is where strict equality operator plays an important role. With this operator, it is possible to return the actual value of the operator without disturbing the operation.

  1. Mention the structures in v that can be regarded as looping structures

They are do-while, While and For loops

  1. Do you think programmers can convert the string to integer in JavaScript?

Yes. It can be done in JavaScript by using a function, parseInt (). With this, the string is taken into the first parameter, then to the next which is regarded as a given string’s base.

  1. What are the two basic groups of data types in javascript?

The two basic groups of data types are Primitive and Reference types.

  1. How do you delete variables in a program? Also, tell if there is any cap on deletion

Variables in a program can be deleted by using the operator, Delete. With this operator, it is possible to delete the objects as well as the variables in a program. However, this operator cannot delete those variables and objects that have been already declared with the keyword var. In order to delete this kind of variables, the user should use another command.

  1. Briefly state when to use Null

Null is basically used when a string does not have any value or object. This function will enable the array to go forward smoothly and executive it’s task reliably. Users need not have to fret while performing this as it does not yield any runtime error at any stage. Moreover, Null can also be used to check whether all the strings have numbers in them or defined variables.

  1. What is undefined value means in JavaScript??

When this error appears on the screen, it basically means that the variable that the user is considering is not present in the code or that the property does not exist. Additionally, the error can also be shown if the variable has not been given any value. These concerns must be addressed before the user goes forward with the program or else, it will have an impact on the entire code.

  1. Difference between the alert box and confirmation box in javascript?

One difference between both pertains to the buttons they have. The Confirmation box has two buttons, namely OK & Cancel. While the Alert box has only one button that is OK. Additionally, there are some differences with regard to a configuration which is hidden for security purposes.

  1. What do you know about escape characters in javascript?

A lot of times, users are required to work with special characters such as single quotes, double quotes, and ampersands for performing special functions. At such instances, the Escape character is used. The users can use a backlash to display it again in any instance. A backlash has to place before the character to display it in a proper way.

  1. Who do you know about JavaScript cookies?

JavaScript cookies are fundamentally tested files of smaller size. They are usually kept in a workstation. These cookies are automatically created when the user opens a webpage for storing the information. It could contain details of what the user is interested in and also information about the username.

  1. Which method is similar to the pop method in JavaScript?

In JavaScript, the shift method is similar to the pop method though there are considerable differences between the two. In the pop method, the last element of the array which is defined is considered generally and the same is returned then. This has the consequence of cutting down the array size. Whereas in Shift method, the first element in the array is considered.

  1. What is called variable typing in javascript?

Variable typing is essentially an approach which enables developers to give a number to any variable which can then be given to a string as well.

  1. Mention the kind of problems that can arise when innerHTML is used in  JavaScript?

A primary issue that can arise relates to content replacement with no message. In this case. Appending approaches can’t be employed which is another setback. In innerHTML, there is no validation and in many instances, it needs to be added to the document that has the consequence of yielding errors on a large scale.

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About Vibhuthi Viswanathan

Vibhuthi is a an avid follower of the latest trends in the world of Technology. Her writing aims to engage and educate the readers on all things Tech. When she is not twirling with words and pauses at SpringPeople, she binge reads popular literature.

Posts by Vibhuthi Viswanathan