gitweb.js: Provide getElementsByClassName method (if it not exists)

The code is simplified and does not support full specification of
native getElementsByClassName method, but implements just subset that
would be enough for gitweb, supporting only single class name.

Signed-off-by: John 'Warthog9' Hawley <warthog9@eaglescrag.net>
Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/static/js/lib/common-lib.js

@@ -88,6 +88,57 @@ function createRequestObject() {
 }
 
 
+/* ............................................................ */
+/* Support for legacy browsers */
+
+/**
+ * Provides getElementsByClassName method, if there is no native
+ * implementation of this method.
+ *
+ * NOTE that there are limits and differences compared to native
+ * getElementsByClassName as defined by e.g.:
+ *   https://developer.mozilla.org/en/DOM/document.getElementsByClassName
+ *   http://www.whatwg.org/specs/web-apps/current-work/multipage/dom.html#dom-getelementsbyclassname
+ *   http://www.whatwg.org/specs/web-apps/current-work/multipage/dom.html#dom-document-getelementsbyclassname
+ *
+ * Namely, this implementation supports only single class name as
+ * argument and not set of space-separated tokens representing classes,
+ * it returns Array of nodes rather than live NodeList, and has
+ * additional optional argument where you can limit search to given tags
+ * (via getElementsByTagName).
+ *
+ * Based on
+ *   http://code.google.com/p/getelementsbyclassname/
+ *   http://www.dustindiaz.com/getelementsbyclass/
+ *   http://stackoverflow.com/questions/1818865/do-we-have-getelementsbyclassname-in-javascript
+ *
+ * See also http://ejohn.org/blog/getelementsbyclassname-speed-comparison/
+ *
+ * @param {String} class: name of _single_ class to find
+ * @param {String} [taghint] limit search to given tags
+ * @returns {Node[]} array of matching elements
+ */
+if (!('getElementsByClassName' in document)) {
+	document.getElementsByClassName = function (classname, taghint) {
+		taghint = taghint || "*";
+		var elements = (taghint === "*" && document.all) ?
+		               document.all :
+		               document.getElementsByTagName(taghint);
+		var pattern = new RegExp("(^|\\s)" + classname + "(\\s|$)");
+		var matches= [];
+		for (var i = 0, j = 0, n = elements.length; i < n; i++) {
+			var el= elements[i];
+			if (el.className && pattern.test(el.className)) {
+				// matches.push(el);
+				matches[j] = el;
+				j++;
+			}
+		}
+		return matches;
+	};
+} // end if
+
+
 /* ............................................................ */
 /* unquoting/unescaping filenames */