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diff --git a/popperjs/package/lib/dom-utils/getViewportRect.js.flow b/popperjs/package/lib/dom-utils/getViewportRect.js.flow
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+++ b/popperjs/package/lib/dom-utils/getViewportRect.js.flow
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+// @flow
+import getWindow from './getWindow';
+import getDocumentElement from './getDocumentElement';
+import getWindowScrollBarX from './getWindowScrollBarX';
+
+export default function getViewportRect(element: Element) {
+  const win = getWindow(element);
+  const html = getDocumentElement(element);
+  const visualViewport = win.visualViewport;
+
+  let width = html.clientWidth;
+  let height = html.clientHeight;
+  let x = 0;
+  let y = 0;
+
+  // NB: This isn't supported on iOS <= 12. If the keyboard is open, the popper
+  // can be obscured underneath it.
+  // Also, `html.clientHeight` adds the bottom bar height in Safari iOS, even
+  // if it isn't open, so if this isn't available, the popper will be detected
+  // to overflow the bottom of the screen too early.
+  if (visualViewport) {
+    width = visualViewport.width;
+    height = visualViewport.height;
+
+    // Uses Layout Viewport (like Chrome; Safari does not currently)
+    // In Chrome, it returns a value very close to 0 (+/-) but contains rounding
+    // errors due to floating point numbers, so we need to check precision.
+    // Safari returns a number <= 0, usually < -1 when pinch-zoomed
+
+    // Feature detection fails in mobile emulation mode in Chrome.
+    // Math.abs(win.innerWidth / visualViewport.scale - visualViewport.width) <
+    // 0.001
+    // Fallback here: "Not Safari" userAgent
+    if (!/^((?!chrome|android).)*safari/i.test(navigator.userAgent)) {
+      x = visualViewport.offsetLeft;
+      y = visualViewport.offsetTop;
+    }
+  }
+
+  return {
+    width,
+    height,
+    x: x + getWindowScrollBarX(element),
+    y,
+  };
+}