Method _shouldPropagateMomentum

src/scrollbar.ts:435–462

(deltaX = 0, deltaY = 0)

  //         1. continuous scrolling is enabled (automatically disabled when overscroll is enabled)
  //         2. scrollbar reaches one side and is not about to scroll on the other direction
  private _shouldPropagateMomentum(deltaX = 0, deltaY = 0): boolean {
    const {
      options,
      offset,
      limit,
    } = this;

    if (!options.continuousScrolling) return false;

    // force an update when scrollbar is "unscrollable", see #106
    if (limit.x === 0 && limit.y === 0) {
      this._updateDebounced();
    }

    const destX = clamp(deltaX + offset.x, 0, limit.x);
    const destY = clamp(deltaY + offset.y, 0, limit.y);
    let res = true;

    // offsets are not about to change
    // `&=` operator is not allowed for boolean types
    res = res && (destX === offset.x);
    res = res && (destY === offset.y);

    // current offsets are on the edge
    res = res && (offset.x === limit.x || offset.x === 0 || offset.y === limit.y || offset.y === 0);

    return res;
  }

  private _render() {
    const {