Web Technology Experts Notes

Thursday, 2 April 2015

Javascript Interview Questions and Answers for Experienced 2

Question: How to set a default parameter value for a JavaScript function?

/** Here email is parameter in which we have set the default value i.e email@domain.com **/
function function1(name, email)
 {
   email = typeof email !== 'undefined' ? email : 'defaultemail@domain.com';
    console.log('name='+name+', Email= '+email);
 }

function1('john','myname@gmail.com');
function1('john');

Queston: How to convert a string to lowercase?

var str='This is testing String';
str = str.toLowerCase();
console.log(str);

Question: How to modify the URL of page without reloading the page?
use pushState javascript function.
For Example:

window.history.pushState('page2', 'This is page Title', '/newpage.php');

Question: How to convert JSON Object to String?

var myobject=['Web','Technology','Experts','Notes']
JSON.stringify(myobject);

Question: How to convert JSON String to Object?

var jsonData = '{"name":"web technology","year":2015}';
var myobject = JSON.parse(jsonData);
console.log(myobject);

Question: How to check an variable is Object OR String OR Array?
Use below function to get Data type of javascript variable.

function checkDataType(someVar){
 result ='String';
    if(someVar instanceof Object){
       result ='Object'
    }
    if($.isArray(someVar)){
      result = 'Array';
    }
return result;
}

var someVar= new Array("Saab", "Volvo", "BMW");
console.log(result);

Question: Can i declare a variable as CONSTANT like in PHP?
No, I think cosntant not exist in javascript.
But you can follow same type convention to declare constant.

var CONSTANT_NAME = "constant value";

Question: How to open URL in new tab in javascript?
use javascript, window.open function.

window.open('http://www.web-technology-experts-notes.in/','_blank');

Question: What is difference between undefined and object?
undefined means some variable's value is not defined yet.
object means variables's value is defined that is either function, object OR array.

With use of below, you can easily determine whether it is object OR NULL.

console.log(typeof(null));      // object
console.log(typeof(undefined)); // undefined

Question: How to get current date in JavaScript?

var today = new Date();
console.log(today);

Question: How do I declare a namespace in JavaScript?

var myNamespace = {

    function1: function() {   },

    function2: function() {    }

    function3: function() {    }
};

myNamespace.function3();

Question: What is the best way to detect a mobile device in jQuery?

if( /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent) ) {

}

Question: How to detect mobiles including ipad using navigator.useragent in javascript?

 if(navigator.userAgent.match(/Android/i) || navigator.userAgent.match(/webOS/i) ||  navigator.userAgent.match(/BlackBerry/i) || navigator.userAgent.match(/iPhone/i)){
        console.log('Calling from Mobile');      
    }else{
    console.log('Calling from Web');      
}

Question: How to detect mobiles including ipad using navigator.useragent in javascript?

 if(navigator.userAgent.match(/Android/i) || navigator.userAgent.match(/webOS/i) ||  navigator.userAgent.match(/BlackBerry/i) || navigator.userAgent.match(/iPhone/i)){
        console.log('Calling from Mobile');      
    }else{
    console.log('Calling from Web');      
}

Wednesday, 1 April 2015

Javascript Interview Questions and Answers for Experienced

Question: What is JavaScript closures? Give an Example?
A closure is an inner function that has access to the outer function's variables known as Closure.

 function function1(x) {
  var tmp = 3;
  function function2(y) {
    console.log(x + y + (++tmp)); // will console 7
  }
  function2(1);
}

function1(2);

Question: What is the function of the var keyword in Javascript?
var is used to create the local variables.
If you're in a function then var will create a local variable.

 var x =10;
function function1(){
var x=20;
}
function1();
alert(x); //10

var x = 10 declares variable x in current scope.
If the declaration appears in a function It is a local variable.
if it's in global scope - a global variable is declared.

 
x =10;
function function1(){
x=20;
}
function1();
alert(x); //20

x=10 declare a global variable.

Question: How can I make a redirect page using jQuery?

 window.location.href = "http://www.web-technology-experts-notes.in/p/sitemap.html";

Question: How can I check if one string contains another substring?
you can use indexOf function,
If string found - It will returns the position of the string in the full string.
If string not found- it will return -1
See Example

 
var haystack = "full-string-here";
var needle = 'string';
if(haystack.indexOf(needle)>=0){
    console.log('String found');
}else{
console.log('String Not found');
}

Question: What is difference between == and === in javascript?
Both are used to check the equality only difference === check with both data type.
For Example

 2=='2' // will return true;
2==='2'// will return false;

Question: Can I comment a JSON file?
No, but you can add a node on root where you can display the information.

Question: How to Check checkbox checked property?

 var checkboxStatus = $('#checkMeOut').prop('checked'); 
if(checkboxStatus){
    console.log('Checkbox is Checked');
}else{
    console.log('Checkbox is Not Checked');
}

Question: How to include a JavaScript file in another JavaScript file?
With use of jQuery, its quite simple, See below:

 $.getScript("my_lovely_script.js", function(){   

});

Question: How to remove single property from a JavaScript object?

var myobject=['Web','Technology','Experts','Notes']
delete myobject['Technology'];

Question: How to add single property from a JavaScript array?

var myobject=['Web','Technology','Experts','Notes']
 myobject.push(' Web Development');

Question: How to empty an array?

var myobject=['Web','Technology','Experts','Notes']
 myobject.length = 0

Question: How to trim string in JavaScript?
You can do in very simple way using jQuery.
See Below:

$.trim('  Web Technology   ');

Question: How do you get a timestamp in JavaScript?

new Date().getTime()

Question: How to use javaScript Loop?

var myobject=['Web','Technology','Experts','Notes']
for (index = 0; index < myobject.length; ++index) {
    console.log(myobject[index]);
}

Question: How to detect an undefined object property in JavaScript?

if (typeof myobject === "undefined") {
    console.log("myobject is undefined");
}

Question: How to validate email address in JavaScript?

function validateEmail(email) {
    var re = /^([\w-]+(?:\.[\w-]+)*)@((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$/i;
    return re.test(email);
}
validateEmail('contactuse@web-technology-experts-notes.in'); // Will return true;

Question: How to capitalize the first letter of string?

function capitalizeFirstLetterOfString(string) {
    return string.charAt(0).toUpperCase() + string.slice(1);
}
capitalizeFirstLetterOfString('web-technology-experts-notes'); //Web-technology-experts-notes

Question: How to get current url in web browser?