React - infinite scrolling (custom component)

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import React, { useRef, useState, useEffect, useMemo } from 'react';

// Calculates element's absolute position.
//
const calculateOffset = (element) => {
    if (element instanceof Window) {
        return 0;
    }
    let result = 0;
    while (element) {
        const value = element.offsetTop;
        if (value) {
            result += value;
        }
        element = element.offsetParent;  // jumps to the next proper parent element
    }
    return result;
};

// Calculates space between elements.
//
const calculateSpace = (aElement, bElement) => {
    const aOffset = calculateOffset(aElement);
    const bOffset = calculateOffset(bElement);
    return bOffset - aOffset;
};

// Calculates container's scroll position.
//
const calculateScroll = (container) => {
    return container.scrollY || container.scrollTop || 0;
};

// Calculates container's inner height.
//
const calculateHeight = (container) => {
    return container.innerHeight || container.clientHeight || 0;
};

// Checks barrier visibility inside container.
//
const checkVisibility = (container, barrier, space) => {
    const barrierTop = calculateSpace(container, barrier);
    const containerScroll = calculateScroll(container);
    const containerHeight = calculateHeight(container);
    if (barrierTop < containerScroll + containerHeight + space) {
        return true;
    }
    return false;
};

// Creates logic that lets to track and control data loading using infinite scolling logic.
//
const createManager = ({
    offset: _offset,
    space: _space,
    loader: _loader,
    container: _container,
    content: _content,
    barrier: _barrier,
    onLoading: _onLoading,
    onLoaded: _onLoaded,
    onError: _onError
}) => {
    let _destroyed = false;
    let _enabled = false;
    let _loading = false;
    const signal = () => {
        if (_loading) {
            return;
        }
        if (_container.current == null || _barrier.current == null || checkVisibility(_container.current, _barrier.current, _space)) {
            _loading = true;
            if (_onLoading) {
                _onLoading();
            }
            const callback = (offset, data, error) => {
                if (_enabled) {
                    _loading = false;
                    try {
                        if (error) {
                            _onError(error);
                        } else {
                            _offset = offset;
                            if (_onLoaded) {
                                _onLoaded(offset, data);
                                if (_enabled === false) {
                                    return;
                                }
                            }
                            if (data && data.length > 0) {
                                setTimeout(signal);
                            }
                        }
                    } catch (e) {
                        console.error(e);
                    }
                }
            };
            try {
                _loader(_offset, callback);
            } catch (e) {
                _loading = false;
                if (_onError) {
                    _onError('Loading error.');
                }
            }
        }
    };
    return {
        signal: () => {
            if (_destroyed) {
                throw new Error('Object has been destroyed.');
            }
            if (_enabled) {
                signal(); 
            }
        },
        enable: () => {
            if (_destroyed) {
                throw new Error('Object has been destroyed.');
            }
            if (_enabled) {
                return;
            }
            _enabled = true;
            _container.current.addEventListener('scroll', signal, false);
            signal();
        },
        disable: () => {
            if (_destroyed) {
                throw new Error('Object has been destroyed.');
            }
            if (_enabled) {
                _enabled = false;
                _container.current.removeEventListener('scroll', signal, false);
            }
        },
        destroy: () => {
            if (_destroyed) {
                return;
            }
            _destroyed = true;
            _enabled = false;
            _container.current.removeEventListener('scroll', signal, false);
        }
    };
};

// Creates function proxy (Source: https://dirask.com/snippets/jmJNN1).
//
const createProxy = () => {
    const state = {
        wrapper: (...args) => {
            if (state.action) {
                return state.action(...args);
            }
            return undefined;
        },
        action: null
    };
    return state;
};

// Privides proxy hook (Source: https://dirask.com/snippets/jmJNN1).
//
const useProxy = (action) => {
    const proxy = useMemo(createProxy, []);
    proxy.action = action;
    return proxy.wrapper;
};

// Component that implements infinite scolling logic.
//
const InfinityScrolling = ({
    containerRef,
    pageSize = 20,
    spaceSize = 100,
    dataLoader,
    itemRenderer
}) => {
    const contentRef = useRef(null);
    const barrierRef = useRef(null);
    const [offset, setOffset] = useState(0);
    const [pages, setPages] = useState(null);
    const [state, setState] = useState(null);
    const loaderProxy = useProxy(dataLoader);
    const manager = useMemo(
        () => {
            return createManager({
                offset: offset,
                space: spaceSize,
                loader: loaderProxy,
                container: containerRef,
                content: contentRef,
                barrier: barrierRef,
                onLoading: () => {
                    setState('Loading...');
                },
                onLoaded: (offset, items) => {
                    if (items.length > 0) {
                        setOffset(offset);
                        setPages(page => page ? [...page, items] : [items]);
                    }
                    if (items.length < pageSize) {
                        setState(null);
                        manager.disable();
                    } else {
                        setState('Click me to continue loading...');
                    }
                },
                onError: (error) => {
                    setState('Loading error! (click me to continue)');
                }
            });
        },
        [containerRef]
    );
    useEffect(
        () => {
            manager.enable();
            return () => {
                manager.disable();
            };
        },
        [containerRef]
    );
    const handleClick = () => manager.signal();
    return (
        <div className="wrapper">
          {pages && (
            <div ref={contentRef} className="content">
              {pages.map((items, index) => {
                  return (
                      <div key={index} className="page">
                        {items.map(itemRenderer)}
                      </div>
                  );
              })}
            </div>
          )}
          {state && (
            <div ref={barrierRef} className="barrier" onClick={handleClick}>
              {state}
            </div>
          )}
        </div>
    );
};



// Usage example:

const App = () => {
    const pageSize = 20;
    const spaceSize = 300;
    const containerRef = useRef(window);
    const loadData = (offset, callback) => {
        const pageNumber = offset + 1;
        fetch(`https://randomuser.me/api/?page=${pageNumber}&results=${pageSize}&seed=abc`)
            .then(response => response.json())
            .then(data => callback(pageNumber, data.results, null))
            .catch((error) => callback(null, null, 'Loading error!'));
    };
    const renderItem = (item, index) => {
        const {first, last} = item.name;
        return (
            <div key={index} className="item">{index}. {first} {last}</div>
        );
    };
    return (
        <div className="app">
          <style>{`
              body { height: 300px }
              .content { background: #fff6c8 }
              .barrier { background: #ffc8c8 }
          `}</style>
          <InfinityScrolling
              containerRef={containerRef}
              pageSize={pageSize}
              spaceSize={spaceSize}
              dataLoader={loadData}
              itemRenderer={renderItem}
          />
        </div>
    );
};

export default App;