vscroll/dist/esm2015/processes/adapter/update.js

Virtual scroll engine

import { BaseAdapterProcessFactory, AdapterProcess, ProcessStatus } from '../misc/index';
import { Item } from '../../classes/item';
import { Direction } from '../../inputs/index';
export default class Update extends BaseAdapterProcessFactory(AdapterProcess.update) {
  static run(scroller, options) {
    const { params } = Update.parseInput(scroller, options);
    if (!params) {
      return;
    }
    const shouldUpdate = Update.doUpdate(scroller, params);
    scroller.workflow.call({
      process: Update.process,
      status: shouldUpdate ? ProcessStatus.next : ProcessStatus.done
    });
  }
  static doUpdate(scroller, params) {
    const { buffer, viewport, state: { fetch }, routines, logger } = scroller;
    if (!buffer.items) {
      logger.log(() => 'no items in Buffer');
      return false;
    }
    const { item: firstItem, index: firstIndex, diff: firstItemDiff } = viewport.getEdgeVisibleItem(buffer.items, Direction.backward);
    const { trackedIndex, toRemove } = buffer.updateItems(params.predicate, (index, data) => new Item(index, data, routines), firstIndex, !!params.fixRight);
    let delta = 0;
    const trackedItem = buffer.get(trackedIndex);
    if (firstItem && firstItem === trackedItem) {
      delta = -buffer.getSizeByIndex(trackedIndex) + firstItemDiff;
    }
    toRemove.forEach(item => item.hide());
    logger.log(() => toRemove.length
      ? 'items to remove: [' + toRemove.map(({ $index }) => $index).join(',') + ']'
      : 'no items to remove');
    if (toRemove.length) { // insertions will be processed on render
      buffer.checkDefaultSize();
    }
    const toRender = buffer.items.filter(({ toInsert }) => toInsert);
    logger.log(() => toRender.length
      ? 'items to render: [' + toRender.map(({ $index }) => $index).join(',') + ']'
      : 'no items to render');
    fetch.update(trackedIndex, delta, toRender, toRemove);
    return !!toRemove.length || !!toRender.length;
  }
}
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