react-infinite/src/computers/arrayInfiniteComputer.js

A browser-ready efficient scrolling container based on UITableView

/* @flow */

var InfiniteComputer = require('./infiniteComputer.js'),
    bs = require('../utils/binaryIndexSearch.js');

class ArrayInfiniteComputer extends InfiniteComputer {
  prefixHeightData: Array<number>;

  constructor(heightData: Array<number>, numberOfChildren: number): void {
    super(heightData, numberOfChildren);
    this.prefixHeightData = this.heightData.reduce((acc, next) => {
      if (acc.length === 0) {
        return [next];
      } else {
        acc.push(acc[acc.length - 1] + next);
        return acc;
      }
    }, []);
  }

  maybeIndexToIndex(index: ?number): number {
    if (typeof index === 'undefined' || index === null) {
      return this.prefixHeightData.length - 1;
    } else {
      return index;
    }
  }

  getTotalScrollableHeight(): number {
    var length = this.prefixHeightData.length;
    return length === 0 ? 0 : this.prefixHeightData[length - 1];
  }

  getDisplayIndexStart(windowTop: number): number {
    var foundIndex = bs.binaryIndexSearch(this.prefixHeightData, windowTop, bs.opts.CLOSEST_HIGHER);
    return this.maybeIndexToIndex(foundIndex);
  }

  getDisplayIndexEnd(windowBottom: number): number {
    var foundIndex = bs.binaryIndexSearch(this.prefixHeightData, windowBottom, bs.opts.CLOSEST_HIGHER);
    return this.maybeIndexToIndex(foundIndex);
  }

  getTopSpacerHeight(displayIndexStart: number): number {
    var previous = displayIndexStart - 1;
    return previous < 0 ? 0 : this.prefixHeightData[previous];
  }

  getBottomSpacerHeight(displayIndexEnd: number): number {
    if (displayIndexEnd === -1) {
      return 0;
    }
    return this.getTotalScrollableHeight() - this.prefixHeightData[displayIndexEnd];
  }
}

module.exports = ArrayInfiniteComputer;