From 83884bdc90c62c785061035bcd39c94eb6e90f52 Mon Sep 17 00:00:00 2001
From: Fabiano Taioli <ftaioli@vista.it>
Date: Wed, 7 Feb 2018 17:46:39 +0100
Subject: [PATCH] element value is not cleared when value valor change to
 undefined

---
 docs/change-log.md         |  1 +
 render/render.js           |  4 ++++
 render/tests/test-input.js | 10 ++++++++++
 3 files changed, 15 insertions(+)

diff --git a/docs/change-log.md b/docs/change-log.md
index 7bdc0478..5df143f6 100644
--- a/docs/change-log.md
+++ b/docs/change-log.md
@@ -43,6 +43,7 @@
 - render: fixed an ommission that caused `oninit` to be called unnecessarily in some cases [#1992](https://github.com/MithrilJS/mithril.js/issues/1992)
 - render: Render state correctly on select change event [#1916](https://github.com/MithrilJS/mithril.js/issues/1916) ([#1918](https://github.com/MithrilJS/mithril.js/pull/1918) [@robinchew](https://github.com/robinchew), [#2052](https://github.com/MithrilJS/mithril.js/pull/2052))
 - render: fix various updateNodes/removeNodes issues when the pool and fragments are involved [#1990](https://github.com/MithrilJS/mithril.js/issues/1990), [#1991](https://github.com/MithrilJS/mithril.js/issues/1991), [#2003](https://github.com/MithrilJS/mithril.js/issues/2003), [#2021](https://github.com/MithrilJS/mithril.js/pull/2021)
+- render: fix element value don't change if new valor is undefined [#2082](https://github.com/MithrilJS/mithril.js/issues/2082)
 
 ---
 
diff --git a/render/render.js b/render/render.js
index aed616aa..9efbde96 100644
--- a/render/render.js
+++ b/render/render.js
@@ -638,6 +638,10 @@ module.exports = function($window) {
 	function setAttr(vnode, key, old, value, ns) {
 		if (key === "key" || key === "is" || isLifecycleMethod(key)) return
 		if (key[0] === "o" && key[1] === "n") return updateEvent(vnode, key, value)
+		if (typeof value === "undefined" && key === "value" && old !== value) {
+			vnode.dom.value = ""
+			return
+		}
 		if ((old === value && !isFormAttribute(vnode, key)) && typeof value !== "object" || value === undefined) return
 		var element = vnode.dom
 		if (key.slice(0, 6) === "xlink:") element.setAttributeNS("http://www.w3.org/1999/xlink", key, value)
diff --git a/render/tests/test-input.js b/render/tests/test-input.js
index 1f9a24d7..c443db1a 100644
--- a/render/tests/test-input.js
+++ b/render/tests/test-input.js
@@ -59,6 +59,16 @@ o.spec("form inputs", function() {
 			o(updated.dom.value).equals("aaa")
 		})
 
+		o("clear element value if vdom value is set to undefined (aka removed)", function() {
+			var input = {tag: "input", attrs: {value: "aaa", oninput: function() {}}}
+			var updated = {tag: "input", attrs: {value: undefined, oninput: function() {}}}
+
+			render(root, [input])
+			render(root, [updated])
+
+			o(updated.dom.value).equals("")
+		})
+
 		o("syncs input checked attribute if DOM value differs from vdom value", function() {
 			var input = {tag: "input", attrs: {type: "checkbox", checked: true, onclick: function() {}}}
 			var updated = {tag: "input", attrs: {type: "checkbox", checked: true, onclick: function() {}}}