Responsive Website Design: JavaScript Interview Questions And Answers

What is javascript?

JavaScript is not a stand-alone programming language like Java. When JavaScript was first

developed, its name was LiveScript, but Netscape contracted with Sun

Microsystems to name it JavaScript.

To run properly, client-side JavaScript is written within HTML documents.

Server-side JavaScript, called LiveWire, can work with back-end server

processes.

JavaScript is a scripting language, JavaScript is object-based, it derives functionality from a

collection of built-in objects. With JavaScript, you can also create your own

objects.JavaScript is platform-independent.

2. Where you place javascript?

You can place javascript in various place in your webpage.

<body>...</body> In body

OR you can declare in both head or body

call javascript through external file to give url

you can give herf="" link after footer or before closing body, it will make fast your website.

3. what are the variables in javascript? and how to declare and define javascript?

javascript having 3 types of variables like Numbers eg. 243, 433.40 etc. Strings of text e.g. "How are you". Boolean e.g. true or false.

there are two types to declare variables:-

Global Variables: A global variable has global scope which means it is defined everywhere in your JavaScript code.

Local Variables: A local variable will be visible only within a function where it is defined. Function parameters are always local to that function.

Example:-

<!--

var myVar = "global"; // Declare a global variable

function checkscope( ) {

var myVar = "local"; // Declare a local variable

document.write(myVar);

}

//-->

</script>

4. How to declare variables?

<!--

var book;

var address;

//-->

</script>

<!--

var book, address;

//-->

</script>

initialization:-

<!--

var book = "javascript";

var address;

address = "bangalore";

//-->

</script>

Some Reserved words in javascript:-

abstract

boolean

break

byte

case

catch

char

class

const

continue

debugger

default

delete

4. What are the operators in javascript?

Arithmetic Operators

Comparision Operators

Logical (or Relational) Operators

Assignment Operators

Conditional (or ternary) Operators

5. What are the conditional statements in javascript?

if statement

if (expression){

Statement(s) to be executed if expression is true

}

if else statement

if (expression){

Statement(s) to be executed if expression is true

}else{

Statement(s) to be executed if expression is false

}

if else if statement

if (expression 1){

Statement(s) to be executed if expression 1 is true

}else if (expression 2){

Statement(s) to be executed if expression 2 is true

}else if (expression 3){

Statement(s) to be executed if expression 3 is true

}else{

Statement(s) to be executed if no expression is true

}

switch case

switch (expression)

{

case condition 1: statement(s)

break;

case condition 2: statement(s)

break;

...

case condition n: statement(s)

break;

default: statement(s)

}

while condition

while (expression){

Statement(s) to be executed if expression is true

}

do while condition

do{

Statement(s) to be executed;

} while (expression);

for loop

for (initialization; test condition; iteration statement){

Statement(s) to be executed if test condition is true

}

for in loop

for (variablename in object){

statement or block to execute

}

6. how to write functions in javascript?

Function Definition:

<!--

function functionname(parameter-list)

{

statements

}

//-->

</script>

Example:-

<!--

function sayHello()

{

alert("Hello there");

}

//-->

</script>

Calling a Function:

example:-

<!--

sayHello();

//-->

</script>

Function Parameters:

example:-

<!--

function sayHello(name, age)

{

alert( name + " is " + age + " years old.");

}

//-->

</script>

The return Statement:

<!--

var result;

result = concatenate('java', 'script');

alert(result );

//-->

</script>

</textarea>

7. what are the events in javascript?

some of the event example:-

onclick Event:

<html>

<head>

<!--

function hi() {

alert("India")

}

//-->

</script>

</head>

<body>

</body>

</html>

onsubmit event:

<html>

<head>

<!--

function hi() {

alert("your value")

}

//-->

</script>

</head>

<body>

</body>

</html>

onmouseover and onmouseout:

<html>

<head>

<!--

function over() {

alert("Mouse Over");

}

function out() {

alert("Mouse Out");

}

//-->

</script>

</head>

<body>

<h2> This is inside the division </h2>

</div>

</body>

</html>

8. how to define cookies in javascript?

syntax:-

document.cookie = "key1=value1;key2=value2;expires=date";

Reading Cookies:

<!--

function ReadCookie()

{

var allcookies = document.cookie;

alert("All Cookies : " + allcookies );

// Get all the cookies pairs in an array

cookiearray = allcookies.split(';');

// Now take key value pair out of this array

for(var i=0; i<cookiearray.length; i++){

name = cookiearray[i].split('=')[0];

value = cookiearray[i].split('=')[1];

alert("Key is : " + name + " and Value is : " + value);

}

//-->

</script>

Setting the Cookies Expiration Date:

<!--

function WriteCookie()

{

var now = new Date();

now.setMonth( now.getMonth() + 1 );

cookievalue = escape(document.myform.customer.value) + ";"

document.cookie="name=" + cookievalue;

document.cookie = "expires=" + now.toUTCString() + ";"

alert("Setting Cookies : " + "name=" + cookievalue );

}

//-->

</script>

Deleting a Cookie:

<!--

function WriteCookie()

{

var now = new Date();

now.setMonth( now.getMonth() - 1 );

cookievalue = escape(document.myform.customer.value) + ";"

document.cookie="name=" + cookievalue;

document.cookie = "expires=" + now.toUTCString() + ";"

alert("Setting Cookies : " + "name=" + cookievalue );

}

//-->

</script>

9. how to page redirect works in javascript?

example:-

<head>

<!--

var browsername=navigator.appName;

if( browsername == "Netscape" )

{

window.location="http://www.location.com/ns.htm";

}

else if ( browsername =="Microsoft Internet Explorer")

{

window.location="http://www.location.com/ie.htm";

}

else

{

window.location="http://www.location.com/other.htm";

}

//-->

</script>

</head>

10. how many ways to show dialog boxes in javascript?

Alert Dialog Box:

<head>

<!--

alert("Warning Message");

//-->

</script>

</head>

Confirmation Dialog Box:

<head>

<!--

var retVal = confirm("Do you want to continue ?");

if( retVal == true ){

alert("User wants to continue!");

return true;

}else{

alert("User does not want to continue!");

return false;

}

//-->

</script>

</head>

Prompt Dialog Box:

<head>

<!--

var retVal = prompt("Enter your name : ", "your name here");

alert("You have entered : " + retVal );

//-->

</script>

</head>

11. how to page printing works in javascript?

<head>

<!--

//-->

</script>

</head>

<body>

<form>

</form>

</body>

12. what are the object methods in javascript?

Syntax:-

objectName.objectProperty = propertyValue;

example:-

document.write("This is test");

The new Operator:

var employee = new Object();

var books = new Array("C++", "Perl", "Java");

var day = new Date("August 15, 1947");

The Object() Constructor:

<html>

<head>

<title>User-defined objects</title>

function book(title, author){

this.title = title;

this.author = author;

}

</script>

</head>

<body>

var myBook = new book("php", "R.K");

document.write("Book title is : " + myBook.title + "<br>");

document.write("Book author is : " + myBook.author + "<br>");

</script>

</body>

</html>

Defining Methods for an Object:

<html>

<head>

<title>User-defined objects</title>

// Define a function which will work as a method

function addPrice(amount){

this.price = amount;

}

function book(title, author){

this.title = title;

this.author = author;

this.addPrice = addPrice; // Assign that method as property.

}

</script>

</head>

<body>

var myBook = new book("php", "R.K");

myBook.addPrice(100);

document.write("Book title is : " + myBook.title + "<br>");

document.write("Book author is : " + myBook.author + "<br>");

document.write("Book price is : " + myBook.price + "<br>");

</script>

</body>

</html>

The with Keyword:

with (object){

properties used without the object name and dot

}

Example:-

<html>

<head>

<title>User-defined objects</title>

// Define a function which will work as a method

function addPrice(amount){

with(this){

price = amount;

}

function book(title, author){

this.title = title;

this.author = author;

this.price = 0;

this.addPrice = addPrice; // Assign that method as property.

}

</script>

</head>

<body>

var myBook = new book("php", "R.K");

myBook.addPrice(100);

document.write("Book title is : " + myBook.title + "<br>");

document.write("Book author is : " + myBook.author + "<br>");

document.write("Book price is : " + myBook.price + "<br>");

</script>

</body>

</html>

13. what are the number properties in javascript?

Syntax:-

var val = new Number(number);

var val = new Boolean(value);

14. what are the string properties in javascript?

syntax:-

var val = new String(string);

15. what are the Array Properties in javascript?

syntax:-

var book = new Array( "java", "php", "wordpress" );

var fruits = [ "eng", "hindi", "science" ];

16. what are the date properties in javascript?

Syntax:-

new Date( )

new Date(milliseconds)

new Date(datestring)

new Date(year,month,date[,hour,minute,second,millisecond ])

17. what are the math functions in javascript?

Example:-

var pi_val = Math.PI;

var sine_val = Math.sin(30);

18. what are the regular expressions in javascript?

syntax:-

var pattern = new RegExp(pattern, attributes);

or simply

var pattern = /pattern/attributes;

19. what is HTML DOM in javascript?

Types:-

Window object:

Document object:

Form object:

Form control elements:

20. what are the Errors and how you handel errors in javascript?

Types

Syntax errors:

Runtime errors:

Logical errors

handle errors

The try...catch...finally Statement:

Example:-

<html>

<head>

<!--

function myFunc()

{

var a = 100;

var b = 0;

try{

if ( b == 0 ){

throw( "Divide by zero error." );

}else{

var c = a / b;

}

}catch ( e ) {

alert("Error: " + e );

}

//-->

</script>

</head>

<body>

<p>Click the following to see the result:</p>

<form>

</form>

</body>

</html>

21. what is validation in javascript?

Basic Validation

Data Format Validation

22. what are the Animations in javascript?<

Fireworks

Fade Effect

Roll-in or Roll-out

Page-in or Page-out

Object movements

Tuesday 17 February 2015

JavaScript Interview Questions And Answers

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