vscroll/dist/esm2015/classes/viewport.js

Virtual scroll engine

import { Paddings } from './paddings';
import { Direction } from '../inputs/index';
export class Viewport {
  constructor(settings, routines, state, logger) {
    this.settings = settings;
    this.routines = routines;
    this.state = state;
    this.logger = logger;
    this.paddings = new Paddings(this.routines, settings);
  }
  reset(startIndex) {
    this.setOffset();
    this.paddings.reset(this.getSize(), startIndex, this.offset);
    this.scrollPosition = this.paddings.backward.size || 0;
    this.state.scroll.reset();
  }
  setPosition(value) {
    const oldPosition = this.scrollPosition;
    if (oldPosition === value) {
      this.logger.log(() => ['setting scroll position at', value, '[cancelled]']);
      return value;
    }
    this.routines.setScrollPosition(value);
    const position = this.scrollPosition;
    this.logger.log(() => [
      'setting scroll position at',
      position,
      ...(position !== value ? [`(${value})`] : [])
    ]);
    return position;
  }
  get scrollPosition() {
    return this.routines.getScrollPosition();
  }
  set scrollPosition(value) {
    this.setPosition(value);
  }
  getSize() {
    return this.routines.getViewportSize();
  }
  getScrollableSize() {
    return this.routines.getScrollerSize();
  }
  getMaxScrollPosition() {
    return this.getScrollableSize() - this.getSize();
  }
  getBufferPadding() {
    return this.getSize() * this.settings.padding;
  }
  getEdge(direction) {
    return this.routines.getViewportEdge(direction);
  }
  setOffset() {
    this.offset = this.routines.getOffset();
  }
  findItemElementById(id) {
    return this.routines.findItemElement(id);
  }
  getEdgeVisibleItem(items, direction) {
    const bwd = direction === Direction.backward;
    const opposite = bwd ? Direction.forward : Direction.backward;
    const viewportEdge = this.getEdge(direction);
    let item, diff = 0;
    for (let i = bwd ? 0 : items.length - 1; bwd ? i <= items.length - 1 : i >= 0; i += bwd ? 1 : -1) {
      const itemEdge = this.routines.getEdge(items[i].element, opposite);
      diff = itemEdge - viewportEdge;
      if ((bwd && diff > 0) || (!bwd && diff < 0)) {
        item = items[i];
        break;
      }
    }
    return { item, index: item ? item.$index : NaN, diff };
  }
}
//# sourceMappingURL=viewport.js.map