Trace a Web Page Load Through the Browser

# Trace a Web Page Load Through the Browser Explain what happens after a user enters a web address and the browser displays an interactive page. Trace the path through name resolution, connection establishment, HTTP, HTML and CSS parsing, JavaScript execution, layout, paint, and composition. ### Constraints & Assumptions - Explain important caches and concurrency without claiming one universal browser implementation. - Distinguish the DOM, CSSOM, render data, painted layers, and composited output. - Address how blocking resources can delay first render or interactivity. ### Clarifying Questions to Ask - Should the answer assume a cold load or warm caches? - Is the page delivered over modern HTTPS and HTTP/2 or HTTP/3? - Is the interviewer interested in networking, rendering performance, or both? ```hint Follow dependencies, not just a fixed list Identify which work can overlap and which resource must be available before the next visible step can proceed. ``` ### What a Strong Answer Covers - URL parsing, DNS, transport security, and HTTP caching. - Streaming parse, preload discovery, CSS and script blocking behavior. - Style calculation, layout, paint, rasterization, and GPU composition. - Main-thread work, later updates, and performance diagnostics. ### Follow-up Questions - Which changes trigger layout versus paint versus composition only? - How would you investigate a page with fast network delivery but slow interactivity?