JavaScript Interview Questions for both Experienced and Fresher
1).What is JavaScript?
Ans:-JavaScript is a scripting language most often used for client-side web development.
2).Difference between JavaScript and Jscript?
Ans:-Both JavaScript and Jscript are almost similar. Java script was developed by Netscape. Microsoft reverse engineered Javascript and called it JScript.
3).How do we add JavaScript onto a web page?
Ans:-
There are serveral way for adding javascript on a web page but there are two way with is commonly userd by developers
If your script code is very short and only for single page then following ways is best
a)You can place <script type="text/javascript"> tag inside the <head> element.
Ans:-Yes!
A function getElementById is not the same as getElementbyID
5).What are the types used in JavaScript?
Ans:-String, Number, Boolean, Function, Object, Null, Undefined.
6).What are the boolean operators sported by JavaScript?
And Operator: &&
Or Operator: ||
Not Operator: !
7).What is the difference between “==” and “===”?
Ans:-
“==” checks equality only,
“===” checks for equality as well as the type.
8).How to access the value of a textbox using JavaScript?
Ans:-
ex:-
There are following way to access the value of the above textbox
var name = document.getElementById('txtFullName').value;
alert(name);
or
we can use the old way
document.forms[0].mybutton.
var name = document.forms[0].FirstName.value;
alert(name);
Note:- this uses the "name" attribute of the element to locate it.
9).What are the way of make comment in Javascript?
Ans:-
// is used for line comments
ex:- var x=10; //comment text
/*
*/ is used for block comments
ex:-
var x= 10; /* this is
block comment example.*/
10).How you will get the CheckBox status whether it is checked or not?
Ans:-
var status = document.getElementById('checkbox1').checked;
alert(status);
it will return true or false
11).How to create arrays in JavaScript?
Ans:-
There are Two way dor create array in Javascript like other languages..
a) first way to create array
Declare Array:-
var names = new Array("Vikas", "Ashish", "Nikhil");
12).If an array with name as "names" contain three elements then how you will print the third element of this array?
Ans:- Print third array element document.write(names[2]);
Note:- array index start with 0
13).How do you submit a form using Javascript?
Ans:-Use document.forms[0].submit();
14).What does isNaN function do?
Ans:-
It Return true if the argument is not a number.
ex:-
true
true
false
15).What is the use of Math Object in Javascript?
Ans:-
The math object provides you properties and methods for mathematical constants and functions.
ex:-
16). What do you understand by this keyword in javascript?
Ans:-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):
17).What does "1"+2+4 evaluate to?
Ans:-Since 1 is a string, everything is a string, so the result is 124.
18).What does 3+4+"7" evaluate to?
Ans:-Since 3 and 4 are integers, this is number arithmetic, since 7 is a string, it’s concatenation, so 77 is the result.
19).How do you change the style/class on any element using javascript?
Ans:-
Ans:- Yes, See example here http://jsfiddle.net/gpDWk/
21).What looping structures are there in JavaScript?
Ans:-for, while, do-while loops
22).what is an object in JavaScript, give an example?
Ans:-
An object is just a container for a collection of named values
Ans:-
24).What is the similarity between 1st and 2nd statement?
1st:- var myString = new String('male'); // An object.
2nd:- var myStringLiteral = 'male'; // Primitive string value, not an object.
Ans:- Both will call String() constructor function
you can confirm it by run the following statement
console.log(myString.constructor, myStringLiteral.constructor);
25).What will be the output of the following statements?
26).Consider the following statements and tell what would be the output of the logs statements?
var price1 = 10;
var price2 = 10;
var price3 = new Number('10'); // A complex numeric object because new was used.
console.log(price1 === price2);
console.log(price1 === price3);
Ans:-
console.log(price1 === price2); // Logs true.
console.log(price1 === price3); /* Logs false because price3 contains a complex number object and price 1
is a primitive value. */
27).What would be the output of the following statements?
When comparing complex objects, they are equal only when they reference the same
object (i.e. have the same address). Two variables containing identical objects are not
equal to each other since they do not actually point at the same object.
28).What would be the output of the following statements?
29).What is this?
var myArray = [[[]]];
Ans:- Three dimantional array
30).Name any two JavaScript functions which are used for convert nonnumeric values into numbers?
Ans:-
Number()
parseInt()
parseFloat()
Ans:-JavaScript is a scripting language most often used for client-side web development.
2).Difference between JavaScript and Jscript?
Ans:-Both JavaScript and Jscript are almost similar. Java script was developed by Netscape. Microsoft reverse engineered Javascript and called it JScript.
3).How do we add JavaScript onto a web page?
Ans:-
There are serveral way for adding javascript on a web page but there are two way with is commonly userd by developers
If your script code is very short and only for single page then following ways is best
a)You can place <script type="text/javascript"> tag inside the <head> element.
Code:
<head>
<title>Page Title</title>
<script language="JavaScript" type="text/javascript">
var name = "Vikas Ahlawta"
alert(name);
</script>
</head>
Code:
<head>
<title>Page Title</title>
<script type="text/javascript" src="myjavascript.js"></script>
</head>
Ans:-Yes!
A function getElementById is not the same as getElementbyID
5).What are the types used in JavaScript?
Ans:-String, Number, Boolean, Function, Object, Null, Undefined.
6).What are the boolean operators sported by JavaScript?
And Operator: &&
Or Operator: ||
Not Operator: !
7).What is the difference between “==” and “===”?
Ans:-
“==” checks equality only,
“===” checks for equality as well as the type.
8).How to access the value of a textbox using JavaScript?
Ans:-
ex:-
Code:
<!DOCTYPE html>
<html>
<body>
Full name: <input type="text" id="txtFullName" name="FirstName" value="Vikas Ahlawat">
</body>
</html>
There are following way to access the value of the above textbox
var name = document.getElementById('txtFullName').value;
alert(name);
or
we can use the old way
document.forms[0].mybutton.
var name = document.forms[0].FirstName.value;
alert(name);
Note:- this uses the "name" attribute of the element to locate it.
9).What are the way of make comment in Javascript?
Ans:-
// is used for line comments
ex:- var x=10; //comment text
/*
*/ is used for block comments
ex:-
var x= 10; /* this is
block comment example.*/
10).How you will get the CheckBox status whether it is checked or not?
Ans:-
var status = document.getElementById('checkbox1').checked;
alert(status);
it will return true or false
11).How to create arrays in JavaScript?
Ans:-
There are Two way dor create array in Javascript like other languages..
a) first way to create array
Declare Array:-
Code:
var names = new Array();
Add Elements in Array:-
names[0] = "Vikas";
names[1] = "Ashish";
names[2] = "Nikhil";
var names = new Array("Vikas", "Ashish", "Nikhil");
12).If an array with name as "names" contain three elements then how you will print the third element of this array?
Ans:- Print third array element document.write(names[2]);
Note:- array index start with 0
13).How do you submit a form using Javascript?
Ans:-Use document.forms[0].submit();
14).What does isNaN function do?
Ans:-
It Return true if the argument is not a number.
ex:-
Code:
document.write(isNaN("Hello")+ "<br>");
document.write(isNaN("2013/06/23")+ "<br>");
document.write(isNaN(123)+ "<br>");
true
true
false
15).What is the use of Math Object in Javascript?
Ans:-
The math object provides you properties and methods for mathematical constants and functions.
ex:-
Code:
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
16). What do you understand by this keyword in javascript?
Ans:-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):
Code:
var obj = { outerWidth : 20 };
function say() {
alert(this.outerWidth);
}
say();//will alert window.outerWidth
say.apply(obj);//will alert obj.outerWidth
17).What does "1"+2+4 evaluate to?
Ans:-Since 1 is a string, everything is a string, so the result is 124.
18).What does 3+4+"7" evaluate to?
Ans:-Since 3 and 4 are integers, this is number arithmetic, since 7 is a string, it’s concatenation, so 77 is the result.
19).How do you change the style/class on any element using javascript?
Ans:-
Code:
document.getElementById(“myText”).style.fontSize = “10";
-or-
document.getElementById(“myText”).className = “anyclass”;
Ans:- Yes, See example here http://jsfiddle.net/gpDWk/
21).What looping structures are there in JavaScript?
Ans:-for, while, do-while loops
22).what is an object in JavaScript, give an example?
Ans:-
An object is just a container for a collection of named values
// Create the man object
Code:
var man = new Object();
man.name = 'Vikas Ahlawat';
man.living = true;
man.age = 27;
Ans:-
Code:
var man = new Object();
man.name = 'Vikas Ahlawat';
man.living = true;
man.age = 27;
man.getName = function() { return man.name;}
console.log(man.getName()); // Logs 'Vikas Ahlawat'.
24).What is the similarity between 1st and 2nd statement?
1st:- var myString = new String('male'); // An object.
2nd:- var myStringLiteral = 'male'; // Primitive string value, not an object.
Ans:- Both will call String() constructor function
you can confirm it by run the following statement
console.log(myString.constructor, myStringLiteral.constructor);
25).What will be the output of the following statements?
Code:
var myString = 'Vikas' // Create a primitive string object.
var myStringCopy = myString; // Copy its value into a new variable.
var myString = null; // Manipulate the value
console.log(myString, myStringCopy);
Ans:- // Logs 'null Vikas'26).Consider the following statements and tell what would be the output of the logs statements?
var price1 = 10;
var price2 = 10;
var price3 = new Number('10'); // A complex numeric object because new was used.
console.log(price1 === price2);
console.log(price1 === price3);
Ans:-
console.log(price1 === price2); // Logs true.
console.log(price1 === price3); /* Logs false because price3 contains a complex number object and price 1
is a primitive value. */
27).What would be the output of the following statements?
var object1 = { same: 'same' };
var object2 = { same: 'same' };
console.log(object1 === object2);
Ans:- // Logs false, JavaScipt does not care that they are identical and of the same object type.When comparing complex objects, they are equal only when they reference the same
object (i.e. have the same address). Two variables containing identical objects are not
equal to each other since they do not actually point at the same object.
28).What would be the output of the following statements?
Code:
var object1 = { same: 'same' };
var object2 = object1;
console.log(object1 === object2);
Ans:- // Logs true29).What is this?
var myArray = [[[]]];
Ans:- Three dimantional array
30).Name any two JavaScript functions which are used for convert nonnumeric values into numbers?
Ans:-
Number()
parseInt()
parseFloat()
Code:
var n1 = Number(“Hello world!”); //NaN
var n2 = Number(“”); //0
var n3 = Number(“000010”); //10
var n4 = Number(true); //1
var n5 = Number(NaN); //NaN
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