| 1 | {"version":3,"file":"useImageExists.js","sources":["../src/lib/cached-map.js","../src/hooks/useImageExists.js"],"sourcesContent":["const A_DAY = 1000 * 60 * 60 * 24\n\nfunction cachedMap({ expireAfter = A_DAY, size = 100 } = {}) {\n const cache = new Map()\n\n // Delete the first (oldest) entry if we are above `size`. `cache.size`\n // should never be greater than `size + 1`, so no need for a loop here.\n function trim() {\n if (cache.size > size) {\n cache.delete(cache.keys().next().value)\n }\n }\n\n // We are using delete() then set() to reset the position everytime the\n // access is refreshed. 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function useImageExists(src, timeUntilFallback = 50) {\n const [exists, setExists] = useState(false)\n const [loading, setLoading] = useState(true)\n const [displayFallback, setDisplayFallback] = useState(false)\n\n useEffect(() => {\n let image = new Image()\n const fallbackTimer = setTimeout(\n () => setDisplayFallback(true),\n timeUntilFallback\n )\n\n const init = () => {\n if (!src) {\n setExists(false)\n setLoading(false)\n return\n }\n\n if (srcCache.get(src)) {\n success()\n return\n }\n\n setExists(false)\n setLoading(true)\n\n // TODO: ensure only one image is loading at a time for a given src.\n image.addEventListener('load', success)\n image.src = src\n }\n\n const success = () => {\n setLoading(false)\n setExists(true)\n srcCache.set(src, true)\n done()\n }\n\n const done = () => {\n clearTimeout(fallbackTimer)\n if (image) {\n image.removeEventListener('load', success)\n image = null\n }\n }\n\n init()\n\n return done\n }, [src, timeUntilFallback])\n\n return useMemo(() 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