The Browser Rendering Process: A Step-by-Step Guide
As web developers, we spend a lot of time writing HTML, CSS, and JavaScript code, but have you ever wondered what happens when the browser receives this code? In this article, we’ll take a deep dive into the browser rendering process, exploring how the browser takes our code and turns it into a beautifully rendered webpage.
The Critical Rendering Path (CRP)
The Critical Rendering Path (CRP) is the sequence of events that occurs between the time the browser receives the initial HTML document and the time it renders the final webpage. The CRP involves several key steps, including:
- DOM Construction: The browser reads the HTML document and constructs a Document Object Model (DOM) tree, which represents the structure of the webpage.
- CSSOM Construction: The browser reads the CSS stylesheets and constructs a CSS Object Model (CSSOM) tree, which represents the styles applied to the webpage.
- JavaScript Execution: The browser executes any JavaScript code, which can modify the DOM and CSSOM trees.
- Layout: The browser calculates the layout of the webpage, determining the position and size of each element.
- Painting: The browser renders the final webpage, using the calculated layout and styles.
Step 1: DOM Construction
When the browser receives the initial HTML document, it begins constructing the DOM tree. This involves parsing the HTML code, identifying elements, and creating nodes in the DOM tree. The DOM tree is a hierarchical representation of the webpage’s structure, with each node representing an element or attribute.
Step 2: CSSOM Construction
Once the DOM tree is constructed, the browser begins constructing the CSSOM tree. This involves parsing the CSS stylesheets, identifying styles, and creating nodes in the CSSOM tree. The CSSOM tree is a hierarchical representation of the styles applied to the webpage,