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* Copyright 2022 Harness Inc. All rights reserved.
* Use of this source code is governed by the PolyForm Shield 1.0.0 license
* that can be found in the licenses directory at the root of this repository, also available at
* https://polyformproject.org/wp-content/uploads/2020/06/PolyForm-Shield-1.0.0.txt.
*/
import { MutableRefObject, useCallback, useEffect, useRef, useState } from 'react'
const DEFAULT_PAGE_SIZE = 10
interface GetItemsWithOffset {
offset?: number
limit?: number
}
interface InfiniteScrollProps {
// getItems is a function promise that will resolve to an array of items to be displayed
getItems: (options: GetItemsWithOffset) => Promise<any>
/*
ref of the element which when visible in the DOM shall trigger the next call
to bring the next set of data. Check the usage in TemplateActivityLog
*/
loadMoreRef: MutableRefObject<Element | null>
// limit prop for defining the size of pagination, default is DEFAULT_PAGE_SIZE
limit?: number
}
interface InfiniteScrollReturnProps {
fetching: boolean
error: string
items: any
hasMore: MutableRefObject<boolean>
offsetToFetch: MutableRefObject<number>
loadItems: () => void
attachRefToLastElement: (index: number) => boolean
}
/*
Hook for infinite scroll
It will only work with NG APIs that support pagination and resolve with this format
{ content: [], empty: false, pageIndex: 1, pageItemCount: 3, pageSize: 10, totalItems: 13, totalPages: 2 }
What will this hook manage?
- Items that are visible on the view. Can be used with any list of items that are resulted from paginated API calls
loadItems
- Fetch data based on a given offset and limit
- Function that accepts a page number/offset variable. It will call the underlying API function with the offset variable
*/
export const useInfiniteScroll = (props: InfiniteScrollProps): InfiniteScrollReturnProps => {
const { getItems, limit = DEFAULT_PAGE_SIZE } = props
const [items, setItems] = useState<any>([])
const [fetching, setFetching] = useState(false)
const [error, setError] = useState('')
const hasMore = useRef(false)
const initialPageLoaded = useRef(false)
const offsetToFetch = useRef(0)
const loadItems = () => {
setFetching(true)
getItems({
offset: offsetToFetch.current,
limit
})
.then(response => {
setFetching(false)
// If the cuurent fetch count exceeds totalItems, set hasMore as false
const canFetchMore =
response.data.totalItems > response.data.pageIndex * response.data.pageSize + response.data.pageItemCount
hasMore.current = canFetchMore
const responseContent = response.data.content
setItems((prevItems: any) => [...prevItems, ...responseContent])
setError('')
})
.catch(err => {
setFetching(false)
setError(err)
setItems([])
})
}
/*
returns true if index is the last element of the list
this is done so that the last element can be noticed by the IntersectionObserver
*/
const attachRefToLastElement = useCallback(
(index: number) => {
return index === items.length - 1 && hasMore.current && !fetching
},
[fetching, hasMore.current]
)
/*
call loadItems() and fetch the next batch of data if the target is now visible in viewport
hasMore is true
fetching is false
Example - the last element of the list. We identify the last element by applying ref in the above callback
*/
const loadMoreCallback = useCallback(
entries => {
const target = entries[0]
if (target.isIntersecting && hasMore.current && !fetching) {
offsetToFetch.current += 1
loadItems()
}
},
[fetching, hasMore.current, loadItems]
)
// Set the intersection observer
useEffect(() => {
// Default options for the IO
// 0.25 threshold means call the callback function when 25% of the target is visible in the DOM
const options = {
threshold: 0.25
}
const observer = new IntersectionObserver(loadMoreCallback, options)
// loadMoreRef is the target element received from props
if (props.loadMoreRef && props.loadMoreRef.current) {
observer.observe(props.loadMoreRef.current)
}
return () => {
props.loadMoreRef?.current && observer.unobserve(props.loadMoreRef?.current)
}
}, [props.loadMoreRef, loadMoreCallback])
// Just to ensure we don't end up fetching multiple times in the initial load
useEffect(() => {
if (initialPageLoaded.current) {
return
}
loadItems()
initialPageLoaded.current = true
}, [loadItems])
return {
fetching,
error,
items,
hasMore,
loadItems,
attachRefToLastElement,
offsetToFetch
}
}
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