getBoundingClientRect.js.flow
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getBoundingClientRect.js.flow
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			// @flow
			import type { ClientRectObject, VirtualElement } from '../types';
			import { isElement, isHTMLElement } from './instanceOf';
			import { round } from '../utils/math';
			import getWindow from './getWindow';
			import isLayoutViewport from './isLayoutViewport';

			export default function getBoundingClientRect(
			element: Element \| VirtualElement,
			includeScale: boolean = false,
			isFixedStrategy: boolean = false
			): ClientRectObject {
			const clientRect = element.getBoundingClientRect();
			let scaleX = 1;
			let scaleY = 1;

			if (includeScale && isHTMLElement(element)) {
			scaleX =
			(element: HTMLElement).offsetWidth > 0
			? round(clientRect.width) / (element: HTMLElement).offsetWidth \|\| 1
			: 1;
			scaleY =
			(element: HTMLElement).offsetHeight > 0
			? round(clientRect.height) / (element: HTMLElement).offsetHeight \|\| 1
			: 1;
			}

			const { visualViewport } = isElement(element) ? getWindow(element) : window;
			const addVisualOffsets = !isLayoutViewport() && isFixedStrategy;

			const x =
			(clientRect.left +
			(addVisualOffsets && visualViewport ? visualViewport.offsetLeft : 0)) /
			scaleX;
			const y =
			(clientRect.top +
			(addVisualOffsets && visualViewport ? visualViewport.offsetTop : 0)) /
			scaleY;
			const width = clientRect.width / scaleX;
			const height = clientRect.height / scaleY;

			return {
			width,
			height,
			top: y,
			right: x + width,
			bottom: y + height,
			left: x,
			x,
			y,
			};
			}