JavaScript - Interview Questions and Answers

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Interview :: JavaScript

41) 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.

42) 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> 

43) Is JavaScript faster than ASP script?

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

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

 <script type="text/javascript">
document.body.bgColor="pink";
</script> 

45) 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.

46)

How to validate a form in JavaScript?

 [removed] function validateform(){ var name=document.myform.name.value; var password=document.myform.password.value;  if (name==null || name=="){   alert("Name can't be blank");   return false; }else if(password.length Password: <input type="password" name="password"><br/> <input type="submit" value="register"> </form>  

47)

How to validate email in JavaScript?

 [removed] function validateemail() { var x=document.myform.email.value; var atposition=x.indexOf("@"); var dotposition=x.lastIndexOf("."); if (atposition=x.length){   alert("Please enter a valid e-mail address \n atpostion:"+atposition+"\n dotposition:"+dotposition);   return false;   } } [removed] <body> <form name="myform"  method="post" action="#" > Email: <input type="text" name="email"><br/>  <input type="submit" value="register"> </form> 

48) 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);   

49) 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:

Using console.log() method
Using debugger keyword

50) 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(); 

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