function arrow()

in js/popper.js [1410:1483]
45 lines of code
11 McCabe index (conditional complexity)

function arrow(data, options) {
  var _data$offsets$arrow;

  // arrow depends on keepTogether in order to work
  if (!isModifierRequired(data.instance.modifiers, 'arrow', 'keepTogether')) {
    return data;
  }

  var arrowElement = options.element;

  // if arrowElement is a string, suppose it's a CSS selector
  if (typeof arrowElement === 'string') {
    arrowElement = data.instance.popper.querySelector(arrowElement);

    // if arrowElement is not found, don't run the modifier
    if (!arrowElement) {
      return data;
    }
  } else {
    // if the arrowElement isn't a query selector we must check that the
    // provided DOM node is child of its popper node
    if (!data.instance.popper.contains(arrowElement)) {
      console.warn('WARNING: `arrow.element` must be child of its popper element!');
      return data;
    }
  }

  var placement = data.placement.split('-')[0];
  var _data$offsets = data.offsets,
      popper = _data$offsets.popper,
      reference = _data$offsets.reference;

  var isVertical = ['left', 'right'].indexOf(placement) !== -1;

  var len = isVertical ? 'height' : 'width';
  var sideCapitalized = isVertical ? 'Top' : 'Left';
  var side = sideCapitalized.toLowerCase();
  var altSide = isVertical ? 'left' : 'top';
  var opSide = isVertical ? 'bottom' : 'right';
  var arrowElementSize = getOuterSizes(arrowElement)[len];

  //
  // extends keepTogether behavior making sure the popper and its
  // reference have enough pixels in conjunction
  //

  // top/left side
  if (reference[opSide] - arrowElementSize < popper[side]) {
    data.offsets.popper[side] -= popper[side] - (reference[opSide] - arrowElementSize);
  }
  // bottom/right side
  if (reference[side] + arrowElementSize > popper[opSide]) {
    data.offsets.popper[side] += reference[side] + arrowElementSize - popper[opSide];
  }
  data.offsets.popper = getClientRect(data.offsets.popper);

  // compute center of the popper
  var center = reference[side] + reference[len] / 2 - arrowElementSize / 2;

  // Compute the sideValue using the updated popper offsets
  // take popper margin in account because we don't have this info available
  var css = getStyleComputedProperty(data.instance.popper);
  var popperMarginSide = parseFloat(css['margin' + sideCapitalized], 10);
  var popperBorderSide = parseFloat(css['border' + sideCapitalized + 'Width'], 10);
  var sideValue = center - data.offsets.popper[side] - popperMarginSide - popperBorderSide;

  // prevent arrowElement from being placed not contiguously to its popper
  sideValue = Math.max(Math.min(popper[len] - arrowElementSize, sideValue), 0);

  data.arrowElement = arrowElement;
  data.offsets.arrow = (_data$offsets$arrow = {}, defineProperty(_data$offsets$arrow, side, Math.round(sideValue)), defineProperty(_data$offsets$arrow, altSide, ''), _data$offsets$arrow);

  return data;
}