fix: account for sorting bug in node 10

__tests__/react/tab.js

@@ -157,7 +157,7 @@ describe("userEvent.tab", () => {
     expect(link).toHaveFocus();
   });
 
-  it("should stay within a focus trab", () => {
+  it("should stay within a focus trap", () => {
     const { getAllByTestId, getByTestId } = render(
       <>
         <div data-testid="div1">
@@ -219,4 +219,29 @@ describe("userEvent.tab", () => {
     // cycle goes back to first element
     expect(checkbox2).toHaveFocus();
   });
+
+  // prior to node 11, Array.sort was unstable for arrays w/ length > 10.
+  // https://twitter.com/mathias/status/1036626116654637057
+  // for this reason, the tab() function needs to account for this in it's sorting.
+  // for example under node 10 in this test:
+  // > 'abcdefghijklmnopqrstuvwxyz'.split('').sort(() => 0).join('')
+  // will give you 'nacdefghijklmbopqrstuvwxyz'
+  it("should support unstable sorting environments like node 10", () => {
+    const letters = "abcdefghijklmnopqrstuvwxyz";
+
+    const { getByTestId } = render(
+      <>
+        {letters.split("").map(letter => (
+          <input key={letter} type="text" data-testid={letter} />
+        ))}
+      </>
+    );
+
+    expect.assertions(26);
+
+    letters.split("").forEach(letter => {
+      userEvent.tab();
+      expect(getByTestId(letter)).toHaveFocus();
+    });
+  });
 });

src/index.js

@@ -1,7 +1,7 @@
 import { fireEvent } from "@testing-library/dom";
 
 function wait(time) {
-  return new Promise(function(resolve) {
+  return new Promise(function (resolve) {
     setTimeout(() => resolve(), time);
   });
 }
@@ -232,21 +232,24 @@ const userEvent = {
     const focusableElements = focusTrap.querySelectorAll(
       "input, button, select, textarea, a[href], [tabindex]"
     );
-    const list = Array.prototype.filter
-      .call(focusableElements, function(item) {
-        return item.getAttribute("tabindex") !== "-1";
-      })
+    let list = Array.prototype.filter.call(focusableElements, function (item) {
+      return item.getAttribute("tabindex") !== "-1";
+    }).map((el, idx) => ({ el, idx }))
       .sort((a, b) => {
-        const tabIndexA = a.getAttribute("tabindex");
-        const tabIndexB = b.getAttribute("tabindex");
-        return tabIndexA < tabIndexB ? -1 : tabIndexA > tabIndexB ? 1 : 0;
-      });
-    const index = list.indexOf(document.activeElement);
+        const tabIndexA = a.el.getAttribute("tabindex");
+        const tabIndexB = b.el.getAttribute("tabindex");
+
+        const diff = tabIndexA - tabIndexB;
+
+        return diff !== 0 ? diff : a.idx - b.idx;
+      })
+
+    const index = list.findIndex(({ el }) => el === document.activeElement);
 
     let nextIndex = shift ? index - 1 : index + 1;
     let defaultIndex = shift ? list.length - 1 : 0;
 
-    const next = list[nextIndex] || list[defaultIndex];
+    const { el: next } = (list[nextIndex] || list[defaultIndex]);
 
     if (next.getAttribute("tabindex") === null) {
       next.setAttribute("tabindex", "0"); // jsdom requires tabIndex=0 for an item to become 'document.activeElement' (the browser does not)