This used to be valid code:
```
class Foo {
constructor() {
this.bar = ‘string’;
}
}
```
This will now fail since ‘bar’ is not explicitly
defined as a field. We now have to write:
```
class Foo {
bar:string; // << REQUIRED
constructor() {
this.bar = ‘string’;
}
}
```
Entry-point to bootstrapping is a rootComponent. The bootstrapping
method, uses the component's selector to find the insertion element in
the DOM, and attaches the component in its ShadowRoot.