code: function count (extent, minZoom, maxZoom, quick) {
    quick = quick || 1000
    let count = 0
  
    // Quick count
    if (quick !== -1) {
      for (const [columns, rows] of levels(extent, minZoom, maxZoom)) {
        count += rows.length * columns.length
      }
      if (count > quick) { return count }
    }
  
    // Accurate count
    count = 0
    const grid = single(extent, minZoom, maxZoom)
    while (true) {
      const {done} = grid.next()
      if (done) { break }
      count++
    }
    return count
  }
docs: Counts the total amount of tiles from a given BBox
  
  @param {BBox|BBox[]|GeoJSON} extent BBox [west, south, east, north] order or GeoJSON Polygon
  @param {number} minZoom Minimum Zoom
  @param {number} maxZoom Maximum Zoom
  @param {number} [quick=1000] Enable quick count if greater than number
  @returns {number} Total tiles from BBox
  @example
  const count = slippyGrid.count([-180.0, -90.0, 180, 90], 3, 8)
  //=count 563136