feat(define): Add support for a static "is" property.

implements #1004

src/api/define.js

@@ -20,7 +20,7 @@ export default function (...args) {
       throw new Error('When passing only one argument to define(), it must be a custom element constructor.');
     } else {
       Ctor = name;
-      name = uniqueId();
+      name = Ctor.is || uniqueId();
     }
   }
 
@@ -41,7 +41,7 @@ export default function (...args) {
   // performance but still falling back to a robust method.
   Ctor[$name] = name;
 
-  // Sipmle define. Not supporting customised built-ins yet.
+  // Simple define. Not supporting customised built-ins yet.
   customElements.define(name, Ctor);
 
   // The spec doesn't return but this allows for a simpler, more concise API.

test/unit/api/define.js

@@ -39,16 +39,36 @@ describe('api/define', () => {
     }).to.not.throw();
   });
 
-  // DEPRECATED
-  it('should take an object and extend Component', () => {
-    expect(define('x-test', class extends Component {}).prototype).to.be.an.instanceof(Component);
+  it('static "is" should be used as "name" argument', () => {
+    const name = 'x-test-api-define-is';
+    const Elem = define(class extends Component {
+      static is = name
+    });
+    const elem = new Elem();
+    expect(elem.localName).to.equal(name);
   });
 
-  it('should be able to take an ES5 extension of Component', () => {
-    expect(define('x-test', class extends Component {}).prototype).to.be.an.instanceof(Component);
+  it('static "is" should not override "name" argument', () => {
+    const name1 = 'x-test-api-define-is-override';
+    const name2 = 'x-test-api-define-is-not-override';
+    const Elem = define(name2, class extends Component {
+      static is = name1
+    });
+    const elem = new Elem();
+    expect(elem.localName).to.equal(name2);
   });
 
-  it('should take a constructor that extends Component', () => {
-    expect(define('x-test', class extends Component {}).prototype).to.be.an.instanceof(Component);
+  describe('deprecated', () => {
+    it('should take an object and extend Component', () => {
+      expect(define('x-test', class extends Component {}).prototype).to.be.an.instanceof(Component);
+    });
+
+    it('should be able to take an ES5 extension of Component', () => {
+      expect(define('x-test', class extends Component {}).prototype).to.be.an.instanceof(Component);
+    });
+
+    it('should take a constructor that extends Component', () => {
+      expect(define('x-test', class extends Component {}).prototype).to.be.an.instanceof(Component);
+    });
   });
 });