Why isn't "export default" recommended in Angular?

Question

According to the Typescript documentation (section "Guidance for structuring modules"):

If you’re only exporting a single class or function, use export default

Just as “exporting near the top-level” reduces friction on your module’s consumers, so does introducing a default export. If a module’s primary purpose is to house one specific export, then you should consider exporting it as a default export. This makes both importing and actually using the import a little easier.

Example:

export default class SomeType {
  constructor() { ... }
}

In the Angular documentation for components (for example) one sees this:

export class HeroListComponent implements OnInit {
  heroes: Hero[];
  selectedHero: Hero;

  constructor(private service: HeroService) { }

  ngOnInit() {
    this.heroes = this.service.getHeroes();
  }

  selectHero(hero: Hero) { this.selectedHero = hero; }
}

Generally, a component's or module's primary purpose is to house one specific export. So, is there a reason why Angular does not use or recommend using export default?

Answer 1

The actual reason is that this doesn't work with the AOT compiler, however it will work with the JIT compiler. So if you are using AOT (or want to use it moving forward), don't do export default. See also here:

Default Exports

Default exports aren't allowed with AoT - they must all be named.

❌ DONT:

import { Component } from '@angular/core';

@Component({
  template: `
    <div class="example">
      Example component!
    </div>
  `
})
export default class ExampleComponent {

}

✅ DO:

import { Component } from '@angular/core';

@Component({
  template: `
    <div class="example">
      Example component!
    </div>
  `
})
export class ExampleComponent {

}