The difference between normal and headless browser - browser

Question

Often I meet PhantomJS to run headless browser , headless browser.
What's the difference between normal (user invoked or regular Selenium webdriver code invoked) and a headless browser?
Besides all, I'd like to make things clear on these browser features:
headers
local storage
cookie

Answer 1

A headless browser is by definition a web browser without a graphical user interface(GUI).
Normally, interaction with a website are done with mouse and keyboard using a browser with a GUI, While most headless browser provides an API to manipulate the page/DOM, download resources etc. So instead of, for example, actually clicking an element with the mouse, a headless browser allows you to click an element by code.
Example of interacting with a page using PhantomJS:
page.evaluate(function() {
//Fill in form on page
document.getElementById('Name').value = 'John Doe';
document.getElementById('Email').value = 'john.doe#john.doe';
//Submit
$('#SubmitButton').click();
});
Headers, Local storage and Cookies work the same way in most headless browsers as they do in regular browsers with a GUI if they are implemented. PhantomJS and HtmlUnit has support for all of these features.
In PhantomJS, you may also add your own cookies. For example, you may copy a cookie from chrome and programmatically add it to the phantomjs browser at runtime. It will automatically be added to page requests for a specific domain.
Adding a cookie to a page before loading it
var webPage = require('webpage');
var page = webPage.create();
phantom.addCookie({
'name' : 'Valid-Cookie-Name', /* required property */
'value' : 'Valid-Cookie-Value', /* required property */
'domain' : 'localhost',
'path' : '/', /* required property */
'httponly' : false,
'secure' : false,
'expires' : (new Date()).getTime() + (1000 * 60 * 60) /* <-- expires in 1 hour */
});
page.open('localhost', function (status) {
//Cookie automatically added to request headers for localhost
...
});
For some runnable examples using PhantomJS, see The phantomjs examples page