As experts, we have compiled a comprehensive list of the top and crucial javascript interview questions and answers for freshers to know. Whether you’re preparing for a job interview or simply looking to expand your JavaScript knowledge, this article will provide you with the javascript technical interview questions and essential information you need to succeed.

Top Javascript interview questions and answers for freshers

As a fresher you need to know the basic interview questions on javascript to be prepared, that’s why we collected a collection of javascript interview questions and answers for you:

1. Can you explain the Differences Between both Java and JavaScript?

This may be the first questions of the javascript interview questions and answers for freshers, to answer say While both Java and JavaScript are programming languages, they have several key differences:

• Purpose: Java is a general-purpose programming language used for building a wide range of applications, from desktop software to enterprise-level applications. JavaScript is used to add interactivity and dynamic behavior to web pages.
• Execution Environment: Java programs are typically compiled and then executed on a Java Virtual Machine (JVM), while JavaScript is an interpreted language that runs directly in the web browser or on a JavaScript runtime, such as Node.js.
• Typing: Java is a statically typed language, which means variables must be declared with a specific data type. JavaScript, however, is a dynamically typed language, allowing for more flexible and dynamic code.
• Object-Oriented Approach: Java is a pure object-oriented language, while JavaScript uses a prototypal object-oriented approach.
• Syntax: Java has a more verbose and strict syntax, while JavaScript has a more concise and flexible syntax.
• Performance: Java is generally faster and more efficient than JavaScript, especially for computationally intensive tasks, due to its compiled nature and static typing.

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2. What are JavaScript Data Types?

One of the common javascript interview questions and answers for freshers is the about JavaScript types, you can answer saying that it has the following data types:

Primitive Data Types

• Number: Represents both integers and floating-point numbers.
• String: Represents textual data.
• Boolean: Represents logical values, either true or false.
• Undefined: Represents a variable that has been declared but not assigned a value, or an object property that does not exist.
• Symbol: Represents a unique and immutable identifier.

Non-Primitive Data Types

• Object: Represents a collection of key-value pairs, including arrays, functions, and more.

3. Which Symbol is Used for Comments in JavaScript?

This is one of the javascript interview questions and answers for freshers about the symbol which is used to create single-line comments, and the /* */ symbols are used to create multi-line comments.

Example:

javascript Copy // This is a single-line comment /* This is a multi-line comment */

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4. What Would be the Result of 3 + 2 + “7”?

This may be one of the javascript interview questions and answers for freshers to answer say The result of 3 + 2 + “7” would be “57”. Here’s how the expression is evaluated:

3 + 2 is evaluated first, resulting in 5.

5 + “7” is then evaluated, where the number 5 is coerced to a string and concatenated with the string “7”, resulting in the string “57”.

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5. What is isNaN Function used for?

This is one of the interview questions about javascript, so answer the question stating that The isNaN function in JavaScript is used to determine whether a value is NaN (Not a Number) or not. 

Example:

javascript Copy console.log(isNaN(42)); // Output: false console.log(isNaN(“hello”)); // Output: true console.log(isNaN(NaN)); // Output: true

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6. Which is Faster in JavaScript and ASP Script?

This one of the javascript interview questions and answers for freshers to answer you would say In general, JavaScript is faster than ASP (Active Server Pages) script. JavaScript is a client-side scripting language, which means it runs directly in the user’s web browser, while ASP is a server-side scripting language, which means it runs on the web server before the page is sent to the client.

The main advantages of JavaScript over ASP script in terms of speed are:

• Client-side Execution: JavaScript code is executed on the client-side, which means it doesn’t need to make a round-trip to the server, reducing latency and improving responsiveness.
• Compiled vs. Interpreted: JavaScript is typically executed by a JavaScript engine, which is a compiled environment, whereas ASP script is interpreted, which can be slower.
• Browser Caching: JavaScript code can be cached by the browser, allowing for faster subsequent executions, whereas ASP script is always executed on the server.
• However, it’s important to note that the overall performance of a web application depends on various factors, such as the complexity of the code, the network conditions, and the server’s processing power.

7. What is Negative Infinity?

This is one of the javascript interview questions and answers for freshers regarding infinity. Negative infinity, or -Infinity, is a special numeric value in JavaScript that represents a value that is less than the smallest possible number. It is typically used to represent a value that is smaller than the lowest possible finite number.

Examples:

javascript Copy console.log(-Infinity); // Output: -Infinity console.log(1 / 0); // Output: Infinity console.log(-1 / 0); // Output: -Infinity

In the last two examples, division by zero results in positive or negative infinity, depending on the sign of the numerator.

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8. Is it Possible to Break JavaScript Code into Several Lines?

If you are looking for interview questions and answers javascript, this question should be on your list. The answer for this question is:

Yes, it is possible to break JavaScript code into several lines. There are a few ways to do this:

Line Breaks: You can simply press the Enter or Return key to break the code into multiple lines.

Example:

javascript Copy let x = 5; let y = 10; let z = x + y;

Semicolons: You can use semicolons (;) to terminate a statement, allowing you to break the code into multiple lines.

Example:

javascript Copy let x = 5; let y = 10; let z = x + y;

Backslash: You can use a backslash (\) at the end of a line to indicate that the statement continues on the next line.

Example:

javascript Copy let x = 5, \     y = 10, \     z = x + y;

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9. Which Company Developed JavaScript?

This is one of the basic javascript interview questions, so you need to know the answers. JavaScript was developed by Brendan Eich at Netscape Communications Corporation (now Mozilla Foundation) in 1995.

Initially, JavaScript was called “Mocha”, then “LiveScript”, and finally “JavaScript” when Netscape and Sun Microsystems (now Oracle) announced a strategic alliance in 1995.

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10. What are Undeclared and Undefined Variables?

This is one of the javascript interview questions and answers for freshers, you can answer saying that:

Undeclared Variables:

Undeclared variables are variables that have not been declared using the let, const, or var keywords. Accessing an undeclared variable will result in a ReferenceError.

Example:

javascript Copy console.log(x); // ReferenceError: x is not defined

Undefined Variables:

Undefined variables are variables that have been declared but not assigned a value. Accessing an undefined variable will result in the value undefined.

Example:

javascript Copy let x; console.log(x); // Output: undefined

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11. Write a JavaScript Code for Adding New Elements Dynamically

This will be definitely one of the javascript interview questions and answers for freshers, so be prepared with this example which shows how to add new elements dynamically using JavaScript:

html Copy <!DOCTYPE html> <html> <head>   <title>Add Elements Dynamically</title> </head> <body>   <h1>Add Elements Dynamically</h1>   <button onclick=”addElement()”>Add Element</button>   <div id=”container”></div>   <script>     function addElement() {       // Create a new div element       const newElement = document.createElement(“div”);       // Set the content and style of the new element       newElement.textContent = “New Element”;       newElement.style.backgroundColor = “lightgray”;       newElement.style.padding = “10px”;       newElement.style.margin = “10px”;       // Append the new element to the container       const container = document.getElementById(“container”);       container.appendChild(newElement);     }   </script> </body> </html> Refresh Show console

In this example, the addElement() function is called when the “Add Element” button is clicked. The function creates a new div element, sets its content and style, and then appends it to the container div using the appendChild() method.

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12. What are Global Variables? How are These Variables Declared, and What are the Problems Associated with Them?

This is one of the javascript interview questions and answers for freshers regarding Global Variables:

Global Variables:

Global variables are variables that are declared outside of any function or block scope. They can be accessed and modified from anywhere in the code, including within functions.

Declaring Global Variables:

In modern JavaScript, global variables are typically declared using the let, const, or var keywords, without any scope qualifier (like window.).

Example:

javascript Copy let globalVar = 42;

Problems with Global Variables:

Using global variables can lead to several problems, including:

• Naming Conflicts: Global variables can easily collide with other variables, leading to unintended behavior and hard-to-debug issues.
• Lack of Encapsulation: Global variables can be accessed and modified from anywhere, making the code harder to reason about and maintain.
• Performance Issues: Accessing global variables can be slower than accessing local variables, especially in large applications.
• Testability and Maintainability: Global variables can make the code harder to test and refactor, as they can have unintended side effects.
• To mitigate these problems, it’s generally recommended to minimize the use of global variables and instead use local variables, object properties, or module-level variables (in the case of modular JavaScript).

13. What Do You Mean by NULL in JavaScript?

this is one of the important javascript interview questions and answers for freshers, because In JavaScript, null is a special value that represents the intentional absence of any object value. It is one of the primitive data types in JavaScript, along with undefined, boolean, number, string, and symbol.

When a variable is assigned the value null, it means that the variable is deliberately set to have no value. This is different from undefined, which represents the absence of a value or the lack of a variable declaration.

Example:

javascript Copy let x = null; console.log(x); // Output: null

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14. What is a Prompt Box?

A prompt box is a JavaScript dialog box that is used to prompt the user to input a value. The prompt box is displayed with a text box, where the user can enter a value, and buttons for the user to confirm or cancel the input.

The prompt() function is used to display a prompt box. It takes two arguments: the message to display to the user and the initial value for the text box.

Example:

javascript Copy let userInput = prompt(“Please enter your name:”, “”); console.log(“User input:”, userInput);

In this example, a prompt box is displayed with the message “Please enter your name:” and an empty initial value. The user’s input is stored in the userInput variable, which is then logged to the console.

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15. How to Delete Property-Specific Values?

This probably will be one of the interview questions on javascript, so here how to answer:

To delete a specific property value in JavaScript, you can use the delete operator.

Example:

javascript Copy const person = {   name: “John Doe”,   age: 30,   occupation: “Software Engineer” }; // Delete the ‘occupation’ property delete person.occupation; console.log(person); // Output: { name: ‘John Doe’, age: 30 }

In this example, the delete operator is used to remove the occupation property from the person object.

Alternatively, you can also set the property value to undefined to effectively remove it, without actually deleting the property.

Example:

javascript Copy const person = {   name: “John Doe”,   age: 30,   occupation: “Software Engineer” }; // Set the ‘occupation’ property to undefined person.occupation = undefined; console.log(person); // Output: { name: ‘John Doe’, age: 30, occupation: undefined }

In this case, the occupation property still exists in the person object, but its value is set to undefined.

16. Explain the Working of Timers in JavaScript. Also Elucidate the Drawbacks of Using the Timer, if Any.

JavaScript provides two main timer functions: setTimeout() and setInterval().

setTimeout():

The setTimeout() function is used to execute a function or piece of code after a specified delay. It takes two arguments: the function to be executed and the delay in milliseconds.

Example:

javascript Copy setTimeout(function() {   console.log(“This will be logged after 3 seconds”); }, 3000);

setInterval():

The setInterval() function is used to execute a function or piece of code repeatedly at a specified interval. It also takes two arguments: the function to be executed and the interval in milliseconds.

Example:

javascript Copy setInterval(function() {   console.log(“This will be logged every 2 seconds”); }, 2000);

Drawbacks of Using Timers:

• Timing Inaccuracy: The actual execution time of the timer-based functions may not be exactly as specified due to factors like system load, event processing, and browser implementation differences.
• Event Loop Blocking: If the timer callback function takes a long time to execute, it can block the event loop, causing other events to be delayed or missed.
• Memory Leaks: If timer-based functions reference external variables or objects without properly cleaning up, it can lead to memory leaks.
• Synchronization Issues: Coordinating multiple timers and ensuring consistent state can be challenging, especially in complex applications.
• To mitigate these drawbacks, it’s important to use timers judiciously, optimize the timer callback functions, and consider alternative approaches, such as using web workers, promises, or observables, depending on the specific use case.

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