import { Story } from './types' ; import { fetchStory , fetchAllNewStories } from './api' ; import { listItem } from './listItem' ; const STORIES_UNDER_FOLD = 20 ; const DEBUG_BATCHES = false ; ( ( ) => { let firstIndexToRender = 0 ; let lastIndexToRender = - 1 ; let shouldFetchMoreItems = false ; const newStoryIDs = [ ] ; const processedIndexes = new Set < number > ( ) ; const workingIndexes = new Set < number > ( ) ; const processedStories = [ ] ; const renderQueue = new Set < number > ( ) ; const list = document . getElementById ( 'list' ) as HTMLElement ; const start = async ( ) => { const stories = await fetchAllNewStories ( ) . catch ( ( ) => { console . error ( 'error in fetching posts' ) ; } ) ; if ( stories ) { newStoryIDs . push ( ... stories ) ; initObserver ( ) ; } } ; const initObserver = ( ) => { const observer = new IntersectionObserver ( onIntersect ) ; const sentinel = document . getElementById ( 'sentinel' ) as HTMLElement ; observer . observe ( sentinel ) ; } ; const onIntersect = ( entries ) => { const entry = entries [ 0 ] ; shouldFetchMoreItems = entry . isIntersecting ; fetchNextBatch ( ) ; } ; const fetchNextBatch = ( ) => { if ( ! shouldFetchMoreItems || workingIndexes . size ) { return ; } lastIndexToRender += STORIES_UNDER_FOLD ; if ( lastIndexToRender >= newStoryIDs . length ) { lastIndexToRender = newStoryIDs . length - 1 ; } for ( let i = firstIndexToRender ; i <= lastIndexToRender ; i ++ ) { workingIndexes . add ( i ) ; } workingIndexes . forEach ( async ( storyIndex ) => { const story = await fetchStory ( newStoryIDs [ storyIndex ] ) . catch ( ( ) => console . error ( `Error fetching story ${ newStoryIDs [ storyIndex ] }` ) ) ; processedStories [ storyIndex ] = story ; addToBatchPipeline ( storyIndex ) ; } ) ; } ; const addToBatchPipeline = ( index ) => { const currentBatch = [ ] ; processedIndexes . add ( index ) ; let i = firstIndexToRender ; for ( ; i <= lastIndexToRender ; i ++ ) { if ( processedIndexes . has ( i ) ) { currentBatch . push ( i ) ; workingIndexes . delete ( i ) ; } else { break ; } } firstIndexToRender = i ; if ( currentBatch . length ) { pushToRenderQueue ( currentBatch ) ; } } ; const pushToRenderQueue = async ( currentBatch ) => { currentBatch . forEach ( renderQueue . add , renderQueue ) ; await new Promise ( requestAnimationFrame ) ; if ( ! renderQueue . size ) { return ; } await render ( ) ; fetchNextBatch ( ) ; } ; const render = async ( ) => { const fragment = new DocumentFragment ( ) ; if ( DEBUG_BATCHES ) { fragment . append ( document . createRange ( ) . createContextualFragment ( '<hr />' ) ) ; } renderQueue . forEach ( index => { const item = processedStories [ index ] ; item && fragment . append ( listItem ( index , item ) ) ; } ) ; list . append ( fragment ) ; renderQueue . clear ( ) ; return true ; } ; start ( ) ; } ) ( ) ;