[fixed] Focus trap when reentering document (#742) (#791)

* [added] Focus trap when reentering document (#742)

Author: Matthew Holloway

Diff for: src/components/ModalPortal.js

@@ -5,6 +5,8 @@ import scopeTab from "../helpers/scopeTab";
 import * as ariaAppHider from "../helpers/ariaAppHider";
 import * as classList from "../helpers/classList";
 import SafeHTMLElement from "../helpers/safeHTMLElement";
+import portalOpenInstances from "../helpers/portalOpenInstances";
+import "../helpers/bodyTrap";
 
 // so that our CSS is statically analyzable
 const CLASS_NAMES = {
@@ -151,6 +153,8 @@ export default class ModalPortal extends Component {
       ariaHiddenInstances += 1;
       ariaAppHider.hide(appElement);
     }
+
+    portalOpenInstances.register(this);
   }
 
   afterClose = () => {
@@ -191,6 +195,8 @@ export default class ModalPortal extends Component {
     if (this.props.onAfterClose) {
       this.props.onAfterClose();
     }
+
+    portalOpenInstances.deregister(this);
   };
 
   open = () => {

Diff for: src/helpers/bodyTrap.js

@@ -0,0 +1,52 @@
+import portalOpenInstances from "./portalOpenInstances";
+// Body focus trap see Issue #742
+
+let before,
+  after,
+  instances = [];
+
+function focusContent() {
+  if (instances.length === 0) {
+    if (process.env.NODE_ENV !== "production") {
+      // eslint-disable-next-line no-console
+      console.warn(`React-Modal: Open instances > 0 expected`);
+    }
+    return;
+  }
+  instances[instances.length - 1].focusContent();
+}
+
+function bodyTrap(eventType, openInstances) {
+  if (!before || !after) {
+    before = document.createElement("div");
+    before.setAttribute("data-react-modal-body-trap", "");
+    before.style.position = "absolute";
+    before.style.opacity = "0";
+    before.setAttribute("tabindex", "0");
+    before.addEventListener("focus", focusContent);
+    after = before.cloneNode();
+    after.addEventListener("focus", focusContent);
+  }
+
+  instances = openInstances;
+
+  if (instances.length > 0) {
+    // Add focus trap
+    if (document.body.firstChild !== before) {
+      document.body.insertBefore(before, document.body.firstChild);
+    }
+    if (document.body.lastChild !== after) {
+      document.body.appendChild(after);
+    }
+  } else {
+    // Remove focus trap
+    if (before.parentElement) {
+      before.parentElement.removeChild(before);
+    }
+    if (after.parentElement) {
+      after.parentElement.removeChild(after);
+    }
+  }
+}
+
+portalOpenInstances.subscribe(bodyTrap);

Diff for: src/helpers/portalOpenInstances.js

@@ -0,0 +1,55 @@
+// Tracks portals that are open and emits events to subscribers
+
+class PortalOpenInstances {
+  constructor() {
+    this.openInstances = [];
+    this.subscribers = [];
+  }
+
+  register = openInstance => {
+    if (this.openInstances.indexOf(openInstance) !== -1) {
+      if (process.env.NODE_ENV !== "production") {
+        // eslint-disable-next-line no-console
+        console.warn(
+          `React-Modal: Cannot register modal instance that's already open`
+        );
+      }
+      return;
+    }
+    this.openInstances.push(openInstance);
+    this.emit("register");
+  };
+
+  deregister = openInstance => {
+    const index = this.openInstances.indexOf(openInstance);
+    if (index === -1) {
+      if (process.env.NODE_ENV !== "production") {
+        // eslint-disable-next-line no-console
+        console.warn(
+          `React-Modal: Unable to deregister ${openInstance} as it was never registered`
+        );
+      }
+      return;
+    }
+    this.openInstances.splice(index, 1);
+    this.emit("deregister");
+  };
+
+  subscribe = callback => {
+    this.subscribers.push(callback);
+  };
+
+  emit = eventType => {
+    this.subscribers.forEach(subscriber =>
+      subscriber(
+        eventType,
+        // shallow copy to avoid accidental mutation
+        this.openInstances.slice()
+      )
+    );
+  };
+}
+
+const portalOpenInstances = new PortalOpenInstances();
+
+export default portalOpenInstances;