JavaScript Interview Questions and Answers for Experienced 2016

Question: How to Get class name using jQuery?

className = $('#IdWhichClassNameWantToGet').attr('class');

Question: How to check a div having class name or Not?

className = $('#IdWhichClassNameWantToCheck').hasClass('hasClass');

Question: How to add a focus on inputbox?

className = $('input#inputBoxId').focus();

Question: How to add X number of days in date?

var dateObject = new Date();
dateObject.setDate(dateObject.getDate()+5); //Add 5 Days

Question: How to add X number of minutes in date?

var dateObject = new Date();
dateObject.setDate(dateObject.getTime()+(30 * 60 * 1000)); //Add 30 Minutes

Question: How to delete an element from Associate Array?

var myArray = new Object();
myArray["firstname"] = "Arun";
myArray["lastname"] = "Kumar";
myArray["age"] = "26";
console.log(myArray); /* Object { firstname="Arun",  lastname="Kumar",  age="26"} */
delete myArray["age"];//Delete an Element
console.log(myArray); /*  Object { firstname="Arun",  lastname="Kumar"} */

Question: How to exit from for loop from JS?
Use return true to exit from loop. For Example:

for (i = 0; i < 5; i++) { 
    if(i>2){
        break;
    }    
}

Question: How to load a noimage.gif, If there we are unable to load images?
Use return true to exit from loop. For Example:

<img onerror="this.onerror=null;this.src=&#39;/images/noimage.gif&#39;;" src="/images/actualimage.jpg" />

Question: How to change the image source with jQuery?
Use return true to exit from loop. For Example:

$("#imageElement").attr("src","/folder/image.jpg");

Question: How to get image Height & Width?

var img = document.getElementById('imageId'); 
var width = img.clientWidth; //this is image width
var height = img.clientHeight; //this is image height

Question: How to Format a number with exactly two decimals in JavaScript?
Use return true to exit from loop. For Example:

var num = 6.42003;
alert(num.toFixed(2)); // "6.42"

Question: How to prevent buttons from submitting forms?
Use return true to exit from loop. For Example:

<form method="post" onsubmit="return saveDatainDb()">
First name:  <input name="firstname" type="text" /><br />
Last name:<br />
<input name="lastname" type="text" />

<input name="submit" type="submit" value="Save Data" />

</form>
<script>
function saveDatainDb(){
    /** Validate , if not valid return false**/
    validation_false=true;
    If(validation_false){
        return false;
    }
    /** Validate , if not valid return false**/


    /** Write here code for AJax call**/
 
    /** Write here code for AJax call**/


}
</script>