1 files changed, 51 insertions, 0 deletions
diff --git a/devtools/shared/dom-helpers.js b/devtools/shared/dom-helpers.js
new file mode 100644
index 0000000000..3646855560
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+++ b/devtools/shared/dom-helpers.js
@@ -0,0 +1,51 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+exports.DOMHelpers = {
+  /**
+   * A simple way to be notified (once) when a window becomes
+   * interactive (DOMContentLoaded).
+   *
+   * It is based on the chromeEventHandler. This is useful when
+   * chrome iframes are loaded in content docshells (in Firefox
+   * tabs for example).
+   *
+   * @param nsIDOMWindow win
+   *        The content window, owning the document to traverse.
+   * @param Function callback
+   *        The method to call when the frame is loaded.
+   * @param String targetURL
+   *        (optional) Check that the frame URL corresponds to the provided URL
+   *        before calling the callback.
+   */
+  onceDOMReady(win, callback, targetURL) {
+    if (!win) {
+      throw new Error("window can't be null or undefined");
+    }
+    const docShell = win.docShell;
+    const onReady = function (event) {
+      if (event.target == win.document) {
+        docShell.chromeEventHandler.removeEventListener(
+          "DOMContentLoaded",
+          onReady
+        );
+        // If in `callback` the URL of the window is changed and a listener to DOMContentLoaded
+        // is attached, the event we just received will be also be caught by the new listener.
+        // We want to avoid that so we execute the callback in the next queue.
+        Services.tm.dispatchToMainThread(callback);
+      }
+    };
+    if (
+      (win.document.readyState == "complete" ||
+        win.document.readyState == "interactive") &&
+      win.location.href == targetURL
+    ) {
+      Services.tm.dispatchToMainThread(callback);
+    } else {
+      docShell.chromeEventHandler.addEventListener("DOMContentLoaded", onReady);
+    }
+  },
+};