Merge pull request #1943 from JacksonJN/fix-null-acitive-element

Fixing IE bug causing active element to be null causing render function to error

docs/change-log.md

@@ -37,6 +37,7 @@
 
 - core: don't call `onremove` on the children of components that return null from the view [#1921](https://github.com/MithrilJS/mithril.js/issues/1921) [octavore](https://github.com/octavore) ([#1922](https://github.com/MithrilJS/mithril.js/pull/1922))
 - hypertext: correct handling of shared attributes object passed to `m()`. Will copy attributes when it's necessary [#1941](https://github.com/MithrilJS/mithril.js/issues/1941) [s-ilya](https://github.com/s-ilya) ([#1942](https://github.com/MithrilJS/mithril.js/pull/1942))
+- Fix IE bug where active element is null causing render function to throw error. ([1943](https://github.com/MithrilJS/mithril.js/pull/1943))
 
 ---
 

render/render.js

@@ -630,7 +630,8 @@ module.exports = function($window) {
 		updateNodes(dom, dom.vnodes, Vnode.normalizeChildren(vnodes), false, hooks, null, namespace === "http://www.w3.org/1999/xhtml" ? undefined : namespace)
 		dom.vnodes = vnodes
 		for (var i = 0; i < hooks.length; i++) hooks[i]()
-		if ($doc.activeElement !== active) active.focus()
+		// document.activeElement can return null in IE https://developer.mozilla.org/en-US/docs/Web/API/Document/activeElement
+		if (active != null && $doc.activeElement !== active) active.focus()
 	}
 
 	return {render: render, setEventCallback: setEventCallback}