Add an example of importing non-browser functions

Closes #208

examples/import_js/defined-in-js.js

@@ -0,0 +1,21 @@
+export function name() {
+  return 'World';
+}
+
+export class MyClass {
+  constructor() {
+    this._number = 42;
+  }
+
+  get number() {
+    return this._number;
+  }
+
+  set number(n) {
+    return this._number = n;
+  }
+
+  render() {
+    return `My number is: ${this.number}`;
+  }
+}