Java Script Interview QUESTIONS

Exam NameJava Script Interview QUESTIONS
DescriptionJava Script Interview QUESTIONS contains the questions from various interview of IT industry.These questions are helpful to crack the IT interview.

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Question: What is JavaScript?

Answer:JavaScript is a scripting language most often used for client-side web development.

Question: What is the difference between JavaScript and Jscript?

Answer:Both JavaScript and Jscript are almost similar. JavaScript was developed by Netscape. Microsoft reverse engineered Javascript and called it JScript.

Question: Is JavaScript case sensitive?

A function getElementById is not the same as getElementbyID.

Question: What are the types used in JavaScript?

Answer:String, Number, Boolean, Function, Object, Null, Undefined.

Question: What is the difference between "==" and "==="?

Answer:"==" checks equality only,
"===" checks for equality as well as the type.

Question: What are the boolean operators supported by JavaScript?

Answer:And Operator: &&
Or Operator: ||
Not Operator: !

Question: How to access the value of a textbox using JavaScript?

Answer:var name = document.getElementById('textboxID').value;

Question: What are the ways of making comments in JavaScript?

Answer:// is used for line comments
ex:- var x=10; //comment text

*/ is used for block comments

Question: How will you get the Checkbox status whether it is checked or not?

Answer:var status = document.getElementById('checkboxID').checked;

Question: How to create arrays in JavaScript?

Answer:There are two ways to create array in JavaScript like other languages:
a) The first way to create array
Declare Array:
var names = new Array();
Add Elements in Array:-
names[0] = "Vikas";
names[1] = "Ashish";
names[2] = "Nikhil";

b) This is the second way:
var names = new Array("Vikas", "Ashish", "Nikhil");

Question: How do you submit a form using JavaScript?

Answer:Use document.forms[0].submit();

Question: What does isNaN function do?

Answer:It returns true if the argument is not a number.

Question: What is the use of Math Object in JavaScript?

Answer:The math object provides you properties and methods for mathematical constants and functions.
var x = Math.PI; // Returns PI
var y = Math.sqrt(16); // Returns the square root of 16
var z = Math.sin(90); Returns the sine of 90

Question: What do you understand by this keyword in JavaScript?

Answer:In JavaScript the this is a context-pointer and not an object pointer. It gives you the top-most context that is placed on the stack. The following gives two different results (in the browser, where by-default the window object is the 0-level context):

var obj = { outerWidth : 20 };

function say() {

say();//will alert window.outerWidth
say.apply(obj);//will alert obj.outerWidth

Question: What does "1"+2+4 evaluate to?

Answer:Since 1 is a string, everything is a string, so the result is 124.

Question: What does 3+4+"7" evaluate to?

Answer:Since 3 and 4 are integers, this is number arithmetic, since 7 is a string, it is concatenation, so 77 is the result.

Question: How do you change the style/class on any element using JavaScript?

Answer:document.getElementById(“myText”).style.fontSize = “10";


document.getElementById(“myText”).className = “anyclass”;

Question: What is an object in JavaScript, give an example?

Answer:An object is just a container for a collection of named values:

var man = new Object(); = 'Vikas Ahlawat'; = true;
man.age = 27;

Question: Name any two JavaScript functions which are used to convert nonnumeric values into numbers?


Question: Does JavaScript Support automatic type conversion, If yes give example.

Answer:Yes! Javascript support automatic type conversion. You should take advantage of it, It is most common way of type conversion used by Javascript developers.

var s = '5';
var a = s*1;
var b = +s;
typeof(s); //"string"
typeof(a); //"number"
typeof(b); //"number"