Ember.js Octane Edition(blog.emberjs.com)

  class OrderLine {
      @observable price = 0
      @observable amount = 1

      @computed get total() {
          return this.price * this.amount
      }
  }

  class OrderLine {
    @tracked price = 0
    @tracked amount = 1

    get total() {
      return this.price * this.amount
    }
  }

  import { observable } from "mobx"
  import { computedFn } from "mobx-utils"

  class Todos {
    @observable todos = []

    getAllTodosByUser = computedFn(function getAllTodosByUser(userId) {
      return this.todos.filter(todo => todo.user === userId))
    })
  }

  import { tracked } from "@glimmer/tracking";

  class Todos {
    @tracked todos = [];

    getAllTodosByUser(userId) {
      return this.todos.filter(todo => todo.user === userId))
    }
  }

    <MyComponent 
      class='foo'         // any html attribute
      @arg={{this.value}} // @ = arg
                      // this = owned by the current context
    />

    (and inside that)

    <div ...attributes> // gets the class attribute
      {{@arg}} // you *know* that @ means it was passed in
    </div>