Tecnoblog's Experience With Discourse Comments

Falco · April 15, 2026, 8:28pm

This is a great idea, I’m adding native support for it

github.com/discourse/discourse

PERF: Lazy load full app embed iframe with IntersectionObserver (#39299)

main ← perf/lazy-load-full-app-embed

merged 02:45PM - 16 Apr 26 UTC

xfalcox

+26 -3

## Summary - Defer loading the Discourse iframe for full app embeds until the u…ser scrolls near it - Feature detect `IntersectionObserver` — fall back to immediate loading if unavailable - Default margin of 1000px to give the heavy PWA time to load before the user reaches it - On by default for `fullApp` embeds, opt out with `lazyLoad: false` - Configurable margin via `lazyLoadMargin` - Show options in the admin embedding code snippet ## How it works The iframe element is appended to the DOM immediately (preserving layout space with `embedHeight`), but its `src` is not set until the `IntersectionObserver` fires. The default 1000px margin gives Discourse a head start on loading before the user actually scrolls to the embed. ```js DiscourseEmbed = { discourseUrl: 'https://forum.example.com/', topicId: 123, fullApp: true, // lazyLoad: false, // disable lazy loading of the iframe // lazyLoadMargin: '1000', // pixels before viewport to start loading }; ``` ## Test plan - [ ] Full app embed below the fold — verify iframe doesn't load until scrolling near it - [ ] Full app embed above the fold — verify it loads immediately (IntersectionObserver fires right away) - [ ] `lazyLoad: false` — verify immediate loading, same as current behavior - [ ] Custom `lazyLoadMargin` — verify the margin is respected - [ ] Standard (non-full-app) embed — verify unchanged behavior (always loads immediately) - [ ] Browser without IntersectionObserver — verify falls back to immediate loading

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Tecnoblog's Experience With Discourse Comments

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