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What is a browser and introduction to how it works?

What is a browser and introduction to how it works?

In the modern-day world, almost everything that is required is happening just with a few touches with our fingertips without going anywhere. Thanks to the internet technologies and services that are built on top of them. Let's explore one of the primitive yet a very powerful tool to date i.e browser. Let's rip it into pieces and understand how that works.

It's a software application which is used to access WorldWideWeb.
Its purpose is to fetch the content from a server and renders it on the user device.

Components of a browser

The key parts of a browser are listed below.

Components.png

  1. User Interface
    • It the entire visible part of a browser which comprises the address bar, forward & backward button, bookmarking menu, etc. It is every other part of the browser except the rendering or paint area (the Area where a web page gets drawn).
  2. Browser engine
    • It works as a translator between Browser UI and rendering engine.
    • It maps the user inputs and interactions to appropriate functions in the rendering engine.
    • Eg: The click of a back button on UI should trigger the render of the previous page. So, this intimation to render engine is handled by browser engine.
  3. Rendering Engine
    • It is responsible to render the requested webpage on to browser screen.
    • Every browser has its own rendering engine. Safari uses WebKit, Firefox uses Gecko & Chrome uses Blink (forked version of WebKit).
  4. Networking
    • It takes care of retrieving the data from the urls with the help of standard internet protocols like HTTP, FTP & SMTP etc. It also handles all the aspects of security and internet communication.
  5. JS Interpreter
    • It is responsible to parse and execute the javascript code present in the website. The final output is sent to the rendering engine for painting it.
    • Chrome uses V8 engine, Firefox uses SpiderMonkey and Edge uses Chakra Javascript engines.
  6. UI Backend
    • UI backend is used for drawing basic widgets; such as a select box, input box, check box, and windows.
    • It is a backend that exposes a generic interface that is not platform specific & internally uses operating system user interface methods.
    • Usually, operating systems have GUI (Graphical user interfaces) & TUI (Text user interface).
    • Eg: The checkbox or list of the same website is rendered differently in iOS, windows & android.
  7. Data Persistence
    • Browsers need a place to store the data locally.
    • Eg: Personalizing site preferences (displaying a user's choice of custom widgets, colour scheme, & font size etc.)
    • There are various storage options available. Local storage, Session Storage, Cookies, WebSQL, IndexedDB, & FileSystem are namely a few.

Workflow

Let's go into a simple workflow of rendering an HTML page.

Workflow.png

  • The HTML file and CSS files fetched from the network layer are sent to respective parsers.
  • The HTML parser will parse the HTML document and will convert it into a tree of nodes called a DOM (Document Object Model) Tree.
  • CSS parser converts the CSS properties of a tag or node into a browser understandable code and will create a CSSOM (Cascading Style Sheet Object Model) Tree.
  • Finally, these two are utilized to create the final Render Tree.
  • Browser by looking at the render tree and metadata of nodes will create a layout with exact dimensions and co-ordinates where each HTML element along with its styles should appear.
  • Paint phase converts each node of the render tree to the pixels on the screen.

HTML to DOM Tree

  • The HTML code will be converted to DOM by a parser. A simple visual representation is shown below.

htmltodom.png

  • In the DOM tree each element is represented as a node.
  • It starts with HTML as the root node and will go on building it as the elements appear to the parsing engine.
  • Below is the diagram that shows how to find everything in a browser.

totalBrowserE.png
So, that ends our brief explanation about the browser and its internal workings.

 
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