JavaScript Interview Questions and Answers (2024)

What is the use of the isNaN function?

JavaScript is faster compared to ASP Script. JavaScript is a client-side scripting language and does not depend on the server to execute. The ASP script is a server-side scripting language always dependable on the server.

What is negative infinity?

The negative infinity is a constant value represents the lowest available value. It means that no other number is lesser than this value. It can be generate using a self-made function or by an arithmetic operation.

Which is faster in JavaScript and ASP script?

The negative infinity is a constant value represents the lowest available value. It means that no other number is lesser than this value. It can be generate using a self-made function or by an arithmetic operation.

How to break JavaScript Code into several lines ?

we will discuss how to break javascript code into several lines. We generally break the code into several lines so that it can be read easily by a third person or the programmer itself.

JavaScript code for adding new elements in a dynamic way?

Javascript is a very important language when it comes to learning how the browser works. Often there are times we would like to add dynamic elements/content to our web pages. This post deals with all of that.

document.createElement("<tagName>");  
// Where <tagName> can be any HTML 
// tagName like div, ul, button, etc.

// newDiv element has been created
For Eg: let newDiv = document.createElement("div");
<!DOCTYPE html> 
<html lang="en"> 

<head> 
	<meta charset="UTF-8"> 
	<meta http-equiv="X-UA-Compatible" content="IE=edge"> 
	<meta name="viewport" content= 
		"width=device-width, initial-scale=1.0"> 

	<style> 
		html, 
		body { 
			height: 100%; 
			width: 100%; 
		} 

		.button { 
			display: flex; 
			align-items: center; 
			justify-content: center; 
		} 

		.tasks { 
			display: flex; 
			justify-content: center; 
			align-items: center; 
			flex-direction: column; 
			margin-top: 20px; 
		} 
	</style> 
</head> 

<body> 
	<div class="button"> 
		<button id="addTask">Add task</button> 
	</div> 
	<div class="tasks"></div> 
	<script type="text/javascript"> 

		// Getting the parent element in which 
		// the new div will be created 
		let task = document.getElementsByClassName("tasks"); 

		// Getting the addTask button element 
		let addTask = document.getElementById("addTask"); 
		
		// Adding onclick event to the button 
		addTask.addEventListener('click', function () { 
	
			// Traversing through collection of HTML 
			// elements (tasks here) 
			for (let i = 0; i < task.length; i++) { 
				
				// New div element is created 
				let newDiv = document.createElement("div"); 
					
				// Setting the attribute of class type to newDiv 
				newDiv.setAttribute("class", "list"); 
					
				// innerText used to write the text in newDiv 
				newDiv.innerText = "New Div created"; 
					
				// Finally append the newDiv to the 
				// parent i.e. tasks 
				task[i].append(newDiv); 
			} 
		}) 
	</script> 
</body> 

</html> 

How to submit a form using JavaScript?

You can use document.form[0].submit() method to submit the form in JavaScript.

What do you mean by the ‘this’ keyword in JavaScript?

‘this’ keyword has different values according to or depending upon where it is used.

If we use it in a method then, this refers to the owner object.
If it is alone, then this refers to the Global object.
If it is used in a function, then this refers to the global object
If it is used in a function, in strict mode, then this remains undefined.
In an event, this refers to that respective element that receives the event.

Explain the working of timers in JavaScript?

The setTimeout(function, delay) function is used to start a timer, which calls a particular function after the, particularly mentioned delay.

The setInterval(function, delay) function is used to repeatedly execute the given function in the said delay and only stops when it is cancelled.

The clearInterval(id) function instructs or indicates the timer to stop (for stopping the given or mentioned function).

The whole timers are operated within a single thread, and for his events might wait or queue up, they wait for their execution.

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