Merge pull request #130 from canjs/old-value

Pass down previous value to onValue callback
canjs · Feb 28, 2018 · 5a66006 · 5a66006
2 parents 7530347 + 61b5e8c
commit 5a66006
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Showing 2 changed files with 15 additions and 3 deletions.
diff --git a/proto-compute.js b/proto-compute.js
@@ -484,8 +484,8 @@ canReflect.assignSymbols(Compute.prototype, {
 	"can.getValue": Compute.prototype.get,
 	"can.valueHasDependencies": hasDependencies,
 	"can.onValue": function onValue(handler, queue) {
-		function translationHandler(ev, newValue) {
-			handler(newValue);
+		function translationHandler(ev, newValue, oldValue) {
+			handler(newValue, oldValue);
 		}
 		singleReference.set(handler, this, translationHandler);
 		//!steal-remove-start

diff --git a/proto-compute_test.js b/proto-compute_test.js
@@ -411,7 +411,6 @@ QUnit.test("can-reflect setValue", function(){
 	QUnit.equal(a.get(), "A", "compute");
 });
 
-
 QUnit.test("registered symbols", function() {
 	var a = new Compute("a");
 
@@ -430,3 +429,16 @@ QUnit.test("registered symbols", function() {
 	a[canSymbol.for("can.offValue")](handler);
 	a.set("d"); // doesn't trigger handler
 });
+
+QUnit.test("canReflect.onValue should get the previous value", function(assert) {
+	var a = new Compute("a");
+	var done = assert.async();
+
+	canReflect.onValue(a, function(newVal, oldVal) {
+		assert.equal(newVal, "b");
+		assert.equal(oldVal, "a");
+		done();
+	});
+
+	a.set("b");
+});