JavaScript Interview Question Set 3

Categories: Java 8(JDK1.8)

What is the difference between View state and Session state?

"View state" is specific to a page in a session whereas "Session state" is specific to a user or browser that can be accessed across all pages in the web application.


What are the pop-up boxes available in JavaScript?

a) Alert Box

b) Confirm Box

c) Prompt Box


 How can we detect OS of the client machine using JavaScript?

The navigator.appVersion string can be used to detect the operating system on the client machine.


How to submit a form using JavaScript by clicking a link?

Let's see the JavaScript code to submit the form by clicking the link.

<form name="myform" action="index.php">  

Search: <input type='text' name='query' />  

<a href="javascript: submitform()">Search</a>  

</form>  

<script type="text/javascript">  

function submitform()  

{  

  document.myform.submit();  

}  

</script>  



Is JavaScript faster than ASP script?

Yes, because it doesn't require web server's support for execution.


 How to change the background color of HTML document using JavaScript?

<script type="text/javascript">  

document.body.bgColor="pink";  

</script>  


How to handle exceptions in JavaScript?

By the help of try/catch block, we can handle exceptions in JavaScript. JavaScript supports try, catch, finally and throw keywords for exception handling.


 What is this keyword in JavaScript?

The this keyword is a reference variable that refers to the current object. For example:

var address=    

{    

company:"Javatpoint",    

city:"Noida",    

state:"UP",    

fullAddress:function()    

{    

return this.company+" "+this.city+" "+this.state;    

}    

};    

var fetch=address.fullAddress();    

document.writeln(fetch);    



What is the requirement of debugging in JavaScript?

JavaScript didn't show any error message in a browser. However, these mistakes can affect the output. The best practice to find out the error is to debug the code. The code can be debugged easily by using web browsers like Google Chrome, Mozilla Firebox.

To perform debugging, we can use any of the following approaches:

a) Using console.log() method

b) Using debugger keyword


What is the use of debugger keyword in JavaScript?

JavaScript debugger keyword sets the breakpoint through the code itself. The debugger stops the execution of the program at the position it is applied. Now, we can start the flow of execution manually. If an exception occurs, the execution will stop again on that particular line.. For example:

function display()  

{  

x = 10;    

y = 15;    

z = x + y;    

debugger;    

document.write(z);    

document.write(a);     

}     

display();  



What is the role of a strict mode in JavaScript?

The JavaScript strict mode is used to generates silent errors. It provides "use strict"; expression to enable the strict mode. This expression can only be placed as the first statement in a script or a function. For example:

"use strict";    

x=10;    

console.log(x);   


What is the use of Math object in JavaScript?

The JavaScript math object provides several constants and methods to perform a mathematical operation. Unlike date object, it doesn't have constructors. For example:

function display()  

{  

  document.writeln(Math.random());  

}  

display();  


What is the use of a Date object in JavaScript?

The JavaScript date object can be used to get a year, month and day. You can display a timer on the webpage by the help of JavaScript date object.

function display()  

{  

  var date=new Date();    

var day=date.getDate();    

var month=date.getMonth()+1;    

var year=date.getFullYear();    

document.write("<br>Date is: "+day+"/"+month+"/"+year);    

}  

display();  


What is the use of a Number object in JavaScript?

The JavaScript number object enables you to represent a numeric value. It may be integer or floating-point. JavaScript number object follows the IEEE standard to represent the floating-point numbers.

function display()  

{  

var x=102;//integer value    

var y=102.7;//floating point value    

var z=13e4;//exponent value, output: 130000    

var n=new Number(16);//integer value by number object    

document.write(x+" "+y+" "+z+" "+n);    

}     

display();  


What is the use of a Boolean object in JavaScript?

The JavaScript Boolean is an object that represents value in two states: true or false. You can create the JavaScript Boolean object by Boolean() constructor.

function display()  

{  

document.writeln(10<20);//true    

document.writeln(10<5);//false     

}     

display();  


What is the use of a TypedArray object in JavaScript?

The JavaScript TypedArray object illustrates an array like a view of an underlying binary data buffer. There is any number of different global properties, whose values are TypedArray constructors for specific element types.

function display()  

{  

var arr1= [1,2,3,4,5,6,7,8,9,10];     

       arr1.copyWithin(2) ;   

       document.write(arr1);    

}  

display();  


What is the use of a Set object in JavaScript?

The JavaScript Set object is used to store the elements with unique values. The values can be of any type i.e. whether primitive values or object references. For example:

function display()  

{  

var set = new Set();    

set.add("jQuery");    

set.add("AngularJS");    

set.add("Bootstrap");    

for (let elements of set) {    

 document.writeln(elements+"<br>");    

}     

}  

display();  

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