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diff --git a/popperjs/package/lib/modifiers/arrow.js.flow b/popperjs/package/lib/modifiers/arrow.js.flow
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+++ b/popperjs/package/lib/modifiers/arrow.js.flow
@@ -0,0 +1,142 @@
+// @flow
+import type { Modifier, ModifierArguments, Padding, Rect } from '../types';
+import type { Placement } from '../enums';
+import getBasePlacement from '../utils/getBasePlacement';
+import getLayoutRect from '../dom-utils/getLayoutRect';
+import contains from '../dom-utils/contains';
+import getOffsetParent from '../dom-utils/getOffsetParent';
+import getMainAxisFromPlacement from '../utils/getMainAxisFromPlacement';
+import { within } from '../utils/within';
+import mergePaddingObject from '../utils/mergePaddingObject';
+import expandToHashMap from '../utils/expandToHashMap';
+import { left, right, basePlacements, top, bottom } from '../enums';
+import { isHTMLElement } from '../dom-utils/instanceOf';
+
+// eslint-disable-next-line import/no-unused-modules
+export type Options = {
+  element: HTMLElement | string | null,
+  padding:
+    | Padding
+    | (({|
+        popper: Rect,
+        reference: Rect,
+        placement: Placement,
+      |}) => Padding),
+};
+
+const toPaddingObject = (padding, state) => {
+  padding =
+    typeof padding === 'function'
+      ? padding({ ...state.rects, placement: state.placement })
+      : padding;
+
+  return mergePaddingObject(
+    typeof padding !== 'number'
+      ? padding
+      : expandToHashMap(padding, basePlacements)
+  );
+};
+
+function arrow({ state, name, options }: ModifierArguments<Options>) {
+  const arrowElement = state.elements.arrow;
+  const popperOffsets = state.modifiersData.popperOffsets;
+  const basePlacement = getBasePlacement(state.placement);
+  const axis = getMainAxisFromPlacement(basePlacement);
+  const isVertical = [left, right].indexOf(basePlacement) >= 0;
+  const len = isVertical ? 'height' : 'width';
+
+  if (!arrowElement || !popperOffsets) {
+    return;
+  }
+
+  const paddingObject = toPaddingObject(options.padding, state);
+  const arrowRect = getLayoutRect(arrowElement);
+  const minProp = axis === 'y' ? top : left;
+  const maxProp = axis === 'y' ? bottom : right;
+
+  const endDiff =
+    state.rects.reference[len] +
+    state.rects.reference[axis] -
+    popperOffsets[axis] -
+    state.rects.popper[len];
+  const startDiff = popperOffsets[axis] - state.rects.reference[axis];
+
+  const arrowOffsetParent = getOffsetParent(arrowElement);
+  const clientSize = arrowOffsetParent
+    ? axis === 'y'
+      ? arrowOffsetParent.clientHeight || 0
+      : arrowOffsetParent.clientWidth || 0
+    : 0;
+
+  const centerToReference = endDiff / 2 - startDiff / 2;
+
+  // Make sure the arrow doesn't overflow the popper if the center point is
+  // outside of the popper bounds
+  const min = paddingObject[minProp];
+  const max = clientSize - arrowRect[len] - paddingObject[maxProp];
+  const center = clientSize / 2 - arrowRect[len] / 2 + centerToReference;
+  const offset = within(min, center, max);
+
+  // Prevents breaking syntax highlighting...
+  const axisProp: string = axis;
+  state.modifiersData[name] = {
+    [axisProp]: offset,
+    centerOffset: offset - center,
+  };
+}
+
+function effect({ state, options }: ModifierArguments<Options>) {
+  let { element: arrowElement = '[data-popper-arrow]' } = options;
+
+  if (arrowElement == null) {
+    return;
+  }
+
+  // CSS selector
+  if (typeof arrowElement === 'string') {
+    arrowElement = state.elements.popper.querySelector(arrowElement);
+
+    if (!arrowElement) {
+      return;
+    }
+  }
+
+  if (false) {
+    if (!isHTMLElement(arrowElement)) {
+      console.error(
+        [
+          'Popper: "arrow" element must be an HTMLElement (not an SVGElement).',
+          'To use an SVG arrow, wrap it in an HTMLElement that will be used as',
+          'the arrow.',
+        ].join(' ')
+      );
+    }
+  }
+
+  if (!contains(state.elements.popper, arrowElement)) {
+    if (false) {
+      console.error(
+        [
+          'Popper: "arrow" modifier\'s `element` must be a child of the popper',
+          'element.',
+        ].join(' ')
+      );
+    }
+
+    return;
+  }
+
+  state.elements.arrow = arrowElement;
+}
+
+// eslint-disable-next-line import/no-unused-modules
+export type ArrowModifier = Modifier<'arrow', Options>;
+export default ({
+  name: 'arrow',
+  enabled: true,
+  phase: 'main',
+  fn: arrow,
+  effect,
+  requires: ['popperOffsets'],
+  requiresIfExists: ['preventOverflow'],
+}: ArrowModifier);