Javascript Interview Questions and Answers for Experienced basic advanced 2015-2016

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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 without reloading the page?

use pushState javascript function. 

For Example:

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

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','xyz@gmail.com');

function1('john');

Question: How to convert JSON String to Object?

var jsonData = '{"name":"27seos","year":2015}';

var myobject = JSON.parse(jsonData);

console.log(myobject);

Question: How to convert Object to String?

var myobject=['27','seos','Notes']

JSON.stringify(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("Raab", "Volvo", "Audi");

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.xyz.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: 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 do I declare a namespace in JavaScript?

var myNamespace = {

    function1: function() {   },

    function2: function() {    }

    function3: function() {    }

};

myNamespace.function3();

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');      

}