[fix] ref.focus() should focus any element type

Ensure that programmatic focus can be moved to any element. Each
instance of a primitive component type (e.g., `View`, `Text`, etc.)
includes a `focus` method. However, on the web only certain elements can
receive programmatic focus by default: those that can also receive
keyboard focus, e.g., `a`, `button`, `input`, etc. All other element
types must set `tabIndex="-1"` in order to be programmatically focusable
without also being focusable via keyboard or mouse.

Fix #1099

packages/react-native-web/src/exports/UIManager/__tests__/index-test.js

@@ -2,8 +2,8 @@
 
 import UIManager from '..';
 
-const createStyledNode = (style = {}) => {
-  const root = document.createElement('div');
+const createStyledNode = (name = 'div', style = {}) => {
+  const root = document.createElement(name);
   Object.keys(style).forEach(prop => {
     root.style[prop] = style[prop];
   });
@@ -18,6 +18,29 @@ const componentStub = {
 };
 
 describe('apis/UIManager', () => {
+  describe('focus', () => {
+    test('sets tabIndex="-1" on elements not programmatically focusable by default', () => {
+      const node = createStyledNode();
+      UIManager.focus(node);
+      expect(node.getAttribute('tabIndex')).toEqual('-1');
+    });
+
+    test('doesn\'t set tabIndex="-1" on elements with an existing tabIndex', () => {
+      const node = createStyledNode();
+      node.tabIndex = 0;
+      UIManager.focus(node);
+      expect(node.getAttribute('tabIndex')).toEqual('0');
+    });
+
+    test('doesn\'t set tabIndex="-1" on elements focusable by default', () => {
+      ['a', 'input', 'select', 'textarea'].forEach(name => {
+        const node = createStyledNode(name);
+        UIManager.focus(node);
+        expect(node.getAttribute('tabIndex')).toBeNull();
+      });
+    });
+  });
+
   describe('updateView', () => {
     test('supports className alias for class', () => {
       const node = createStyledNode();
@@ -27,7 +50,7 @@ describe('apis/UIManager', () => {
     });
 
     test('adds correct DOM styles to existing style', () => {
-      const node = createStyledNode({ color: 'red' });
+      const node = createStyledNode('div', { color: 'red' });
       const props = { style: { marginTop: 0, marginBottom: 0, opacity: 0 } };
       UIManager.updateView(node, props, componentStub);
       expect(node.getAttribute('style')).toEqual(
@@ -36,7 +59,7 @@ describe('apis/UIManager', () => {
     });
 
     test('replaces input and textarea text', () => {
-      const node = createStyledNode();
+      const node = createStyledNode('textarea');
       node.value = 'initial';
       const textProp = { text: 'expected-text' };
       const valueProp = { value: 'expected-value' };

packages/react-native-web/src/exports/UIManager/index.js

@@ -37,6 +37,13 @@ const measureLayout = (node, relativeToNativeNode, callback) => {
   }
 };
 
+const focusableElements = {
+  A: true,
+  INPUT: true,
+  SELECT: true,
+  TEXTAREA: true
+};
+
 const UIManager = {
   blur(node) {
     try {
@@ -46,6 +53,13 @@ const UIManager = {
 
   focus(node) {
     try {
+      const name = node.nodeName;
+      // A tabIndex of -1 allows element to be programmatically focused but
+      // prevents keyboard focus, so we don't want to set the value on elements
+      // that support keyboard focus by default.
+      if (node.getAttribute('tabIndex') == null && focusableElements[name] == null) {
+        node.setAttribute('tabIndex', '-1');
+      }
       node.focus();
     } catch (err) {}
   },