Add Element.closest

dom.js

@@ -501,6 +501,21 @@
     }
   }
 
+  // Element.closest
+  // https://developer.mozilla.org/en-US/docs/Web/API/Element/closest
+  if (window.Element && !Element.prototype.closest) {
+    Element.prototype.closest = function(s) {
+      var matches = (this.document || this.ownerDocument).querySelectorAll(s),
+          i,
+          el = this;
+      do {
+        i = matches.length;
+        while (--i >= 0 && matches.item(i) !== el) {};
+      } while ((i < 0) && (el = el.parentElement)); 
+      return el;
+    };
+  }
+
   function mixin(o, ps) {
     if (!o) return;
     Object.keys(ps).forEach(function(p) {

tests/dom_tests.js

@@ -174,6 +174,13 @@ QUnit.test("matches", function(assert) {
   assert.ok(document.querySelector('#baz').matches('.beta'));
 });
 
+QUnit.test("closest", function(assert) {
+  assert.equal(document.querySelector('#bar').closest('#foo'), document.querySelector('#foo'));
+  assert.equal(document.querySelector('#baz').closest('#foo'), document.querySelector('#foo'));
+  assert.equal(document.querySelector('#foo').closest('#foo'), document.querySelector('#foo'));
+  assert.notOk(document.querySelector('#baz').closest('#bat'));
+});
+
 QUnit.test('Mixin ParentNode: prepend()', function(assert) {
   var elem = document.querySelector('#mixin-parentnode');
   var orig = elem.innerHTML;