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Ishan Bagchi
Ishan Bagchi

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Important Interview Questions: Javascript Version - Part 1

Here are some of the javascript questions asked in interviews.

What is JavaScript?

Javascript is a scripting language that adds functionality to a web page for example javascript adds animations on clicking a button. JavaScript is also an Object-based Programming language.

State the difference between javascript and java

Java JavaScript
It is Object-Oriented Programming language It is an Object-based Scripting language
Java applications can run in any virtual machine(JVM) or browser JavaScript code used to run only in the browser, but now it can run on the server via Node.js
Supports multithreading Does not support multithreading

What are Javascript datatypes?

Following are the JavaScript Data types:

  • Number
  • String
  • Boolean
  • Arrays
  • Object
  • Undefined
  • Null

What is the use of the isNaN function?

This function returns true when the argument passed is not a number.

Between JavaScript and an ASP script, which is faster?

Javascript is a client-side language and does not require assistance from the web. On the other hand, ASP is a server side language and hence is slower than JavaScript. (For details on ASP check the doccumentation.)

What is Negative Infinity?

A number in JavaScript which is derived by dividing a negative number by zero is called Negative Infinity.

Is it possible to break JavaScript Code into several lines?

In a string statement, a backslash can be given at the end of the 1st line to move the rest in the next line.

doccument.write('First line. \Second line.')
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And if you change to a new line when not within a string statement, then javaScript ignores the break in the line.

const number =
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Which company developed JavaScript?

Netscape is a software company that developed JavaScript.

What are undefined and undeclared variables?

Undefined occurs when a variable has been declared but no value is assigned to it. Undefined is not a keyword.

Undeclared occurs when we try to access a variable that is not defined using the const, var or let keyword.

let undefinedVariable

console.log(undefinedVariable) // undefined
console.log(undeclaredVariable) // ReferenceError: undeclaredVariable is not defined
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Write the code for adding new elements dynamically?

<!DOCTYPE html>
<html lang="en">
    <title>Dynamic elements</title> 
    <script type="text/javascript"> 
        function addNode() { 
            var newP = document.createElement("p"); 
            var textNode = document.createTextNode(" This is a new text node"); 
    <p id="oldP">firstP<p> 
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Top comments (2)

rgelman profile image

Don't work in a place that asks "Which company developed JavaScript" πŸ˜…

One more: what is the result of "0.1 + 0.2"?

ishanbagchi profile image
Ishan Bagchi

0.1 + 0.2 is not equal to 0.3. It is not a problem of the language but it is because of the system. Other languages rounds the number, but JavaScript doesn't.