I have listed 10 most commonly asked JavaScript interview questions and answers. If you’re attending Front-End developer interview, this is a must read article!

RECOMMENDED READING : HTML5 interview Questions and Answers on DGlobaltech

Latest : Drupal interview Questions and Answers

(1) What is event bubbling and capturing in JavaScript?

Event bubbling is series of events when : An event is triggered on the inner most element first and then it triggers on the parent elements in nested order.

DOM elements could be nested inside each other. The handler of the parent works even if you click on it’s child. Event bubbling can make this happen.

Event Capturing is the opposite of bubbling where the event is triggered on the outer most element and then it triggers the inner children in nested order.

(2) What is a closure in JavaScript?

JavaScript allows you to declare a function within another function, and the local variables still can be accessible even after returning from the function you called.

In other words, a closure is the local variables for a function which is kept alive after the function has returned.

An example :

function goodMorning(name) {
var text = ‘Good Morning ‘ + name; // local variable
var goodMorningAlert = function() { alert(text); }
return sayAlert;
}

var goodMorningAlert2 = goodMorning(‘Bob’);
goodMorningAlert2();

In the example above, when goodMorningAlert2() will be executed, you will see output as an alert with “Good Morning Bob”.

In short, in JavaScript, if you use the function keyword inside another function, you are creating a closure.

(3) What is a callback function in JavaScript?
(4) What are various methods you’d use to embed JavaScript onto a webpage?
(5) What is the difference between GET and POST methods in HTML form?

When you use a GET method, key and values will be appended at the end of the URL as a query string. GET method is not recommended to use when you are passing sensitive data over the internet.

While sending data, the GET method appends the data to the URL. And the length of a URL is limited. Maximum URL length is 2048 characters supported by latest browsers.

POST is used to pass sensitive data as it’s not appended and displayed within the URL. There is no limitation as to how much data can be passed using a POST method.

                                                                    Continue Reading Next 5 Questions