Template polypill: (a) support template.cloneNode and (b) document.importNode(template). Supports nested templates.

src/Template/Template.js

@@ -61,15 +61,52 @@ if (typeof HTMLTemplateElement === 'undefined') {
             },
             configurable: true
           });
+
+          template.cloneNode = function(deep) {
+            return HTMLTemplateElement.cloneNode(this, deep);
+          };
+
         } catch (err) {
           canDecorate = false;
         }
       }
 
+      var nativeCloneNode = Node.prototype.cloneNode;
+
+      HTMLTemplateElement.cloneNode = function(template, deep) {
+        var clone = nativeCloneNode.call(template);
+        this.decorate(clone);
+        if (deep) {
+          // NOTE: use native clone node to make sure CE's wrapped
+          // cloneNode does not cause elements to upgrade.
+          clone.content.appendChild(
+              nativeCloneNode.call(template.content, true));
+          // these two lists should be coincident
+          var s$ = template.content.querySelectorAll(TEMPLATE_TAG);
+          var t$ = clone.content.querySelectorAll(TEMPLATE_TAG);
+          for (var i=0, l=t$.length, t, s; i<l; i++) {
+            s = s$[i];
+            t = t$[i];
+            this.decorate(s);
+            t.parentNode.replaceChild(s.cloneNode(true), t);
+          }        
+        }
+        return clone;
+      };
+
       // bootstrap recursively
       HTMLTemplateElement.bootstrap(template.content);
     };
 
+    var originalImportNode = document.importNode;
+
+    // clone instead of importing <template>
+    document.importNode = function(element, deep) {
+      return (element.localName === TEMPLATE_TAG) ?
+        HTMLTemplateElement.cloneNode(element, deep) :
+        originalImportNode.call(document, element, deep);
+    };
+
     /**
       The `bootstrap` method is called automatically and "fixes" all
       <template> elements in the document referenced by the `doc` argument.

tests/Template/tests.html

@@ -61,8 +61,97 @@
           div.innerHTML = s;
           // innerHTML is properly escaped
           assert.equal(imp.innerHTML, escaped);
-          assert.equal(imp.content.childNodes.length, div.childNodes.length);
+          assert.equal(imp.content.textContent, div.textContent);
         });
+
+        test('clone', function() {
+          var imp = document.createElement('template');
+          var s = '<div>Hi</div>';
+          imp.innerHTML = s;
+          var clone = imp.cloneNode();
+          assert.notEqual(clone, imp, 'element is not cloned');
+          assert.isDefined(clone.content, 'cloned template content dne');
+          assert.equal(clone.content.childNodes.length, 0, 
+              'non-deep cloned template.content is not empty');
+          var deepClone = imp.cloneNode(true);
+          assert.equal(deepClone.content.childNodes.length, 1, 
+              'deep cloned template.content is empty');
+          assert.notEqual(imp.content.firstChild, deepClone.content.firstChild, 
+              'cloned content is not different from source');
+        });
+
+        test('nested clone', function() {
+          var imp = document.createElement('template');
+          var s = 'a<template id="a">b<template id="b">c<template id="c">d</template></template></template>';
+          imp.innerHTML = s;
+          var clone = imp.cloneNode();
+          assert.notEqual(clone, imp, 'element is not cloned');
+          assert.isDefined(clone.content, 'cloned template content dne');
+          assert.equal(clone.content.childNodes.length, 0, 
+              'non-deep cloned template.content is not empty');
+          var deepClone = imp.cloneNode(true);
+          assert.equal(deepClone.content.childNodes.length, 2, 
+              'deep cloned template.content is empty');
+          assert.notEqual(imp.content.firstChild, deepClone.content.firstChild, 
+              'cloned content is not different from source');
+          var nested = deepClone.content.lastChild;
+          assert.isDefined(nested.content, 'nested cloned template content dne');
+          assert.equal(nested.content.childNodes.length, 2, 
+              'deep cloned template.content is empty');
+          nested = nested.content.lastChild;
+          assert.isDefined(nested, 'nested cloned template content dne');
+          assert.equal(nested.content.childNodes.length, 2, 
+              'deep cloned template.content is empty');
+          nested = nested.content.lastChild;
+          assert.isDefined(nested, 'nested cloned template content dne');
+          assert.equal(nested.content.childNodes.length, 1, 
+              'deep cloned template.content is empty');
+        });
+
+        test('importNode', function() {
+          var imp = document.createElement('template');
+          var s = '<div>Hi</div>';
+          imp.innerHTML = s;
+          var clone = document.importNode(imp);
+          assert.notEqual(clone, imp, 'element is not cloned');
+          assert.isDefined(clone.content, 'cloned template content dne');
+          assert.equal(clone.content.childNodes.length, 0, 
+              'non-deep cloned template.content is not empty');
+          var deepClone = document.importNode(imp, true);
+          assert.equal(deepClone.content.childNodes.length, 1, 
+              'deep cloned template.content is empty');
+          assert.notEqual(imp.content.firstChild, deepClone.content.firstChild, 
+              'cloned content is not different from source');
+        });
+
+        test('nested importNode', function() {
+          var imp = document.createElement('template');
+          var s = 'a<template id="a">b<template id="b">c<template id="c">d</template></template></template>';
+          imp.innerHTML = s;
+          var clone = document.importNode(imp);
+          assert.notEqual(clone, imp, 'element is not cloned');
+          assert.isDefined(clone.content, 'cloned template content dne');
+          assert.equal(clone.content.childNodes.length, 0, 
+              'non-deep cloned template.content is not empty');
+          var deepClone = document.importNode(imp, true);
+          assert.equal(deepClone.content.childNodes.length, 2, 
+              'deep cloned template.content is empty');
+          assert.notEqual(imp.content.firstChild, deepClone.content.firstChild, 
+              'cloned content is not different from source');
+          var nested = deepClone.content.lastChild;
+          assert.isDefined(nested.content, 'nested cloned template content dne');
+          assert.equal(nested.content.childNodes.length, 2, 
+              'deep cloned template.content is empty');
+          nested = nested.content.lastChild;
+          assert.isDefined(nested, 'nested cloned template content dne');
+          assert.equal(nested.content.childNodes.length, 2, 
+              'deep cloned template.content is empty');
+          nested = nested.content.lastChild;
+          assert.isDefined(nested, 'nested cloned template content dne');
+          assert.equal(nested.content.childNodes.length, 1, 
+              'deep cloned template.content is empty');
+        });
+
       });
     </script>
   </body>