typescript - Angular2 - should private variables be accessible in the template?

Question

If a variable is declared private on a component class, should I be able to access it in the template of that component?

@Component({
  selector: 'my-app',
  template: `
    <div>
      <h2>{{title}}</h2>
      <h2>Hello {{userName}}</h2> // I am getting this name
    </div>
  `,
})
export class App {
  public title = 'Angular 2';
  private userName = "Test Name"; //declared as private
}

Answer 1

No, you shouldn't be using private variables in your templates.

While I like the drewmoore's answer and see perfect conceptual logic in it, implementationwise it's wrong. Templates do not exist within component classes, but outside of them. Take a look at this repo for the proof.

The only reason why it works is because TypeScript's private keyword doesn't really make member private. Just-in-Time compilation happens in a browser at runtime and JS doesn't have any concept of private members (yet?). Credit goes to Sander Elias for putting me on the right track.

With ngc and Ahead-of-Time compilation, you'll get errors if you try accessing private members of the component from template. Clone demonstration repo, change MyComponent members' visibility to private and you will get compilation errors, when running ngc. Here is also answer specific for Ahead-of-Time compilation.