1 files changed, 55 insertions, 0 deletions
diff --git a/devtools/client/responsive/utils/message.js b/devtools/client/responsive/utils/message.js
new file mode 100644
index 0000000000..d06f95ab27
--- /dev/null
+++ b/devtools/client/responsive/utils/message.js
@@ -0,0 +1,55 @@
+/* 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";
+
+const REQUEST_DONE_SUFFIX = ":done";
+
+function wait(win, type) {
+  return new Promise(resolve => {
+    const onMessage = event => {
+      if (event.data.type !== type) {
+        return;
+      }
+      win.removeEventListener("message", onMessage);
+      resolve();
+    };
+    win.addEventListener("message", onMessage);
+  });
+}
+
+/**
+ * Post a message to some window.
+ *
+ * @param win
+ *        The window to post to.
+ * @param typeOrMessage
+ *        Either a string or and an object representing the message to send.
+ *        If this is a string, it will be expanded into an object with the string as the
+ *        `type` field.  If this is an object, it will be sent as is.
+ */
+function post(win, typeOrMessage) {
+  // When running unit tests on XPCShell, there is no window to send messages to.
+  if (!win) {
+    return;
+  }
+
+  let message = typeOrMessage;
+  if (typeof typeOrMessage == "string") {
+    message = {
+      type: typeOrMessage,
+    };
+  }
+  win.postMessage(message, "*");
+}
+
+function request(win, type) {
+  const done = wait(win, type + REQUEST_DONE_SUFFIX);
+  post(win, type);
+  return done;
+}
+
+exports.wait = wait;
+exports.post = post;
+exports.request = request;