The Browser Critical Rendering Path
The Browser Critical Rendering Path
MediumFrontend0% accepted
A page feels slow to first paint. Walk through the browser's Critical Rendering Path from receiving HTML to pixels on screen. Cover: DOM + CSSOM construction, why CSS is render-blocking, where JavaScript blocks parsing, the render tree, layout (reflow) vs paint vs composite, and 3 concrete techniques to speed up first paint.
Approach
HTML→DOM, CSS→CSSOM, combine→Render Tree, Layout→Paint→Composite. CSS blocks render; sync JS blocks parsing. Defer JS, inline critical CSS, minimise reflows.
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