From 16719e1d070c9713c35984a42f3f86161f16b25e Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonygarnockjones@gmail.com>
Date: Mon, 19 Nov 2018 22:21:36 +0000
Subject: [PATCH] UIChangeableProperty

---
 packages/driver-browser-ui/src/index.js    | 17 +++++++++++++++++
 packages/driver-browser-ui/src/protocol.js |  5 +++++
 2 files changed, 22 insertions(+)

diff --git a/packages/driver-browser-ui/src/index.js b/packages/driver-browser-ui/src/index.js
index 490b4cb..b160f87 100644
--- a/packages/driver-browser-ui/src/index.js
+++ b/packages/driver-browser-ui/src/index.js
@@ -366,6 +366,23 @@ function splitClassValue(v) {
 
 ///////////////////////////////////////////////////////////////////////////
 
+spawn named 'UIChangeablePropertyFactory' {
+  during Observe(P.UIChangeableProperty($selector, $property, _))
+  spawn named ['UIChangeableProperty', selector, property] {
+    on start selectorMatch(document, selector).forEach((node) => {
+      react {
+        field this.value = node[property];
+        assert P.UIChangeableProperty(selector, property, this.value);
+        const handlerClosure = Dataspace.wrapExternal((e) => { this.value = node[property]; });
+        on start eventUpdater('change', handlerClosure, true)(node);
+        on stop eventUpdater('change', handlerClosure, false)(node);
+      }
+    });
+  }
+}
+
+///////////////////////////////////////////////////////////////////////////
+
 function escapeDataAttributeName(s) {
   // Per https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/dataset,
   // the rules seem to be:
diff --git a/packages/driver-browser-ui/src/protocol.js b/packages/driver-browser-ui/src/protocol.js
index 85f05fa..47b717c 100644
--- a/packages/driver-browser-ui/src/protocol.js
+++ b/packages/driver-browser-ui/src/protocol.js
@@ -63,6 +63,11 @@ module.exports.UIAttribute = UIAttribute;
 assertion type UIProperty(selector, property, value);
 module.exports.UIProperty = UIProperty;
 
+// Assertion. For clients to monitor the values of properties that,
+// when changed, emit 'change' events.
+assertion type UIChangeableProperty(selector, property, value);
+module.exports.UIChangeableProperty = UIChangeableProperty;
+
 // Messages.
 // NOTE: These do not treat "class" specially!
 message type SetAttribute(selector, attribute, value);