JavaScript Interview Questions and Answers: Comprehensive Guide for Success

JavaScript Interview Questions and Answers: Comprehensive Guide for Success

 

Popular computer language JavaScript is employed to add dynamic interactivity to webpages. Today, JavaScript is one of the most in-demand skills globally, opening up a tonne of work chances for both new graduates and seasoned experts. This JavaScript interview questions guide can aid you in obtaining your ideal position if you are interested in a career in JavaScript and are preparing for a job interview. The following sections make up this JavaScript interview questions and answers blog:

 

JavaScript Interview Questions for Beginners

 

What are the major advantages of JavaScript?

How can you differentiate JavaScript from Java?

JavaScript code is entirely written in text and only needs to be translated. Contrarily, Java needs to be compiled. They are employed in a variety of projects. While JavaScript is mostly used on HTML texts and browsers, Java is utilised to create applications for devices or browsers.

 

How to create an object in JavaScript?

Use the new keyword along with the Object() function Object() { [native code] } to create an object like follows: person: const new Object(); Now, we must add the following properties to this object: person.

 

Tell some of the widely used JavaScript testing frameworks.

Top Javascript Testing Frameworks

•   MochaJS.
•   Jest.
•   Jasmine.
•   Karma.
•   Puppeteer (Node Library)
•   NightwatchJS.
•   Cypress.

 

JavaScript Functions – What do you know about it?

Similar to a procedure in JavaScript, a function must accept an input and provide an output with an evident relationship between the input and the output in order to be considered a function. A procedure is a collection of statements that performs an action or calculates a result.

 

What are some of the JavaScript data types?

There are 7 types of JavaScript errors: Syntax error, Reference Error, Type Error, Evaluation Error, RangeError, URI Error and Internal Error. Errors in Javascript can be handled using the try… catch… finally construct as well as the throw operator.

 

Define JavaScript ?

A dynamic computer programming language is called JavaScript. Its implementations enable client-side script to interact with users and create dynamic pages, and it is most frequently used as a component of web pages. It is an object-oriented programming language that may be interpreted.

 

Is JavaScript programming language or scripting language?

JavaScript is a dynamic scripting language that supports prototype-based object building, to put it briefly. Intentionally emulating both Java and C++’s core syntax helps to minimise the number of novel ideas that must be learned in order to master the language.

 

What is the difference between primitives and objects in javascript ?

A new value can be assigned to the variable, but unlike with arrays or objects, the primitive’s current value cannot be modified. The primary distinction between the two categories is so as follows: Object Types are mutable, while Primitive Types are immutable.

 

What are the types of JavaScript Function Scope?

JavaScript has 3 types of scope:

• Block scope.
• Function scope.
• Global scope.

 

What is the difference between JavaScript keywords – var and let.

In javascript, the terms var and let are both used to declare variables, but var is function scoped whereas let is block scoped.

 

What do you mean by Hoisting in Javascript?

Prior to running the code, the interpreter appears to relocate the definition of functions, variables, or classes to the top of their scope. This process is known as JavaScript hoisting.

 

What does DOM mean in JavaScript?

Web documents have a programming interface called the Document Object Model (DOM). So that software can alter the document’s structure, appearance, and content, it serves as a representation of the page. Because the document is represented by the DOM as nodes and objects, programming languages can communicate with the page.

 

What is the use of BOM in JavaScript?

The term “Browser Object Model” (BOM) is a web browser-specific abbreviation for all objects that the web browser exposes. The BOM permits “interaction” between JavaScript and the browser.

 

What is a JavaScript string?

Strings in JavaScript are used to store and modify text. A string in JavaScript is defined as zero or more characters enclosed in quotations.

 

Define the usage of Set objects in JavaScript.

Collections of values are called set objects. In the Set’s collection, a value may only appear once; it is exclusive. A set’s components can be iterated through in insertion order.

 

Intermediate-Level JavaScript Interview Questions 

 

How to formulate a cookie using Javascript?

To create a cookie using JavaScript, you can utilize the document.cookie property. Here’s an example of how to formulate a cookie:

javascript
// Function to set a cookie
function setCookie(name, value, daysToExpire) {
var cookie = name + “=” + encodeURIComponent(value);

if (daysToExpire) {
var expirationDate = new Date();
expirationDate.setDate(expirationDate.getDate() + daysToExpire);
cookie += “; expires=” + expirationDate.toUTCString();
}

document.cookie = cookie;
}

// Usage example
setCookie(“username”, “John Doe”, 7); // Sets a cookie named “username” with the value “John Doe” that expires in 7 days

In the setCookie function, you provide the name, value, and optional number of days for the cookie to expire. The function encodes the value using encodeURIComponent to handle special characters properly. If an expiration duration is specified, it calculates the expiration date and appends it to the cookie string. Finally, it assigns the cookie to the document.cookie property to store it in the browser.

Note that the document.cookie property allows you to access and modify all cookies associated with the current domain. If you want to retrieve or delete a cookie, you need to handle the document.cookie string accordingly.

 

In HTML, how many ways are there to involve JS?

In HTML, there are three primary ways to involve JavaScript:

Inline JavaScript

You can include JavaScript code directly within an HTML file using the <script> tag. The JavaScript code is placed between the opening <script> tag and the closing </script> tag. For example:
html

<script>
// Inline JavaScript code
console.log(“Hello, world!”);
</script>

External JavaScript File

You can link an external JavaScript file to your HTML document using the <script> tag’s src attribute. The external JavaScript file contains the JavaScript code that will be executed. This approach allows for better code organization and reusability.

For example:
html<script src=”script.js”></script>

Event Attributes

HTML elements can have event attributes that invoke JavaScript code when specific events occur. These attributes start with “on” followed by the event name. For example, onclick, onload, onsubmit, etc. You can define JavaScript code directly within the event attribute. For example:
html
<button onclick=”myFunction()”>Click me</button>

<script>
function myFunction() {
// Event attribute JavaScript code
console.log(“Button clicked!”);
}
</script>

It’s worth noting that it’s generally considered a best practice to separate JavaScript code from HTML for maintainability and code organization. Using external JavaScript files is preferred when dealing with complex or reusable code. However, inline JavaScript and event attributes can be handy for quick, small-scale interactions.

 

What is the major difference between == and === operators?

The == operator determines whether two values are equivalent. The!= operator determines if two values are equal or not. It is also known as the “loose equality operator” since it tends to transform the data types of operands when two operands aren’t of the same data type in order to carry out the comparison. This is because it tests abstract equality.

 

What is isNaN in javascript ?

NaN stands for “Not-a-Number” in JavaScript. If a value is NaN, the isNaN() method returns true. Prior to being tested, the value is converted to a number via the isNaN() method.

 

Which method is used to remove focus from the specified object in Javascript?

In Javascript, the Blur method shifts the emphasis away from the provided object.

 

What is event bubbling in terms of Javascript?

The DOM has a concept known as event bubbling (Document Object Model). The event bubbles up (or you could say is transmitted or propagated) to the element’s parent and grandparent elements in the DOM tree until it reaches the root element once an element receives an event.

 

Explain pop() and shift() method in javascript?

While pop() removes the last element from an array, shift() removes the first element from an array. The array’s removed first member is what the Shift() function returns. The pop() method transforms the removed element array, whereas this function returns undefined if the array is empty.

 

What are the disadvantages of using innerHTML in JavaScript?

But utilising innerHTML in JavaScript has several drawbacks. Using JavaScript’s innerHTML property has the following drawbacks: innerHTML use is really sluggish: The process of using innerHTML is much slower as its contents as slowly built, also already parsed contents and elements are also re-parsed which takes time

 

What is the role of event.preventdefault() method in javascript?

If the event is cancellable, the preventDefault() method will do so, stopping the default action associated with the event. This can be helpful, for instance, when you want to stop a form from being submitted when you click the “Submit” button.

 

Advanced Level JavaScript Interview Questions and Answers

 

What is the difference between call and apply in javascript ?

The call() method accepts parameters independently, which is the distinction. The array of arguments is passed to the apply() method. If you wish to use an array instead of an argument list, the apply() method is very useful.

 

How do you empty an array in JavaScript?

In JavaScript, there are several ways to empty an array. The quickest way to empty an array with JavaScript is to assign the array to an empty array. When the length property in JavaScript is set to 0, the array is cleared. JavaScript’s splice() method can be used to remove one or more elements from an array.

 

Define Escape character in JavaScript ?

The symbol used to start an escape command in order to carry out any activity is called a “escape character.” They are characters that can be read in a variety of ways other than the ones we intended. The backslash (‘/’) is used as an escape character in Javascript.

 

What does wrap do in JavaScript?

You can add common logic to functions you do not control, like native and external functions, by wrapping JavaScript functions. Many JavaScript libraries, including the TrackJS agents, depend on wrappers to carry out their functions.

 

What is the procedure to remove duplicate values from a Javascript array?

JavaScript’s filter() method generates a fresh array of elements based on whether they satisfy the given criterion. The elements for which true is returned will be the only ones included. By modifying our condition, we can easily eliminate duplicate values from the array.

 

How to check mouse events in JavaScript?

Utilizing the onmousedown () event

Alternatively, we could state that it happens whenever the left mouse button is pressed over the chosen object. InnerHTML = “Left mouse button clicked” if (e. button == 0)

 

How do we get the primitive value of a string in javascript?

A String object’s primitive value is returned as a string data type via the function valueOf() { [native code] }() function of the String class. String. prototype. function toString() { [native code] }() and this value are interchangeable.

 

Explain Loops in JavaScript.?

In JavaScript, loops are used to carry out repeated operations based on a condition. Typically, conditions return true or false. Until the specified condition returns false, a loop will keep executing.

 

Name the method we can use to read and write a file in JavaScript?

Javascript’s readFile() and rs. writeFile() functions are used to read and write files. A built-in method called fs. readFile() is used to read the file.

 

What is the difference between attribute and property in javascript?

An element in JavaScript (actually the DOM) has attributes and properties. Although the names are frequently used interchangeably, they refer to two distinct concepts. When rendered in the DOM, an attribute is in its initial state. The present condition is a property.

 

What is a callback in JavaScript?

A function that is supplied as an argument to another function is called a callback. A function may call another function using this method. After another function has completed, a callback function may continue to run.

 

When to use JSON Stringify?

Javascript’s JSON. Stringify() technique is used to convert it into a JSON string. It is frequently necessary to serialise data to strings while creating a JavaScript application in order to store it in a database, send it to an API, or send it to a web server.

 

What is memoization in javascript ?

Memorization is a programming optimization approach that speeds up applications by increasing their efficiency. This is accomplished by caching calculation results so that they can be retrieved from the cache rather than having to be recalculated as needed.

 

What is the use of constructor function in javascript?

A function Object() { [native code] } is a unique function that generates and initialises a class-specific object instance. When an object is created with JavaScript using the new keyword, the function Object() { [native code] } is invoked. A constructor’s function is to build a new object and set values for any properties of an existing object that already exist.

 

What are undeclared and undefined variables in javascript?

Undefined: This condition happens when a variable is declared but not given a value. A keyword is not undefined. When we attempt to access a variable that has not yet been initialised or declared using the var or const keyword, we get the undeclared error.

 

What is a prompt box in javascript?

If you want the user to enter a value before seeing a page, a prompt box is frequently utilised. The user must click “OK” or “Cancel” to continue after providing an input value when a prompt box appears. The input value is returned to the box if the user hits “OK.”

 

In conclusion, this comprehensive guide on JavaScript interview questions and answers serves as a valuable resource for job seekers and interviewers looking to excel in JavaScript interviews. Covering a wide range of JavaScript topics, from the fundamentals to advanced concepts, this guide equips individuals with the knowledge and confidence needed to succeed. By exploring this resource, you can strengthen your understanding of JavaScript, improve your programming skills, and confidently tackle JavaScript interview questions. Whether you’re a beginner or an experienced developer, this guide provides valuable insights to enhance your JavaScript expertise and excel in your interviews.