mobx

class Todo {
    id = Math.random();
    constructor(content) {
		extendObservable(this, {
			content: content,
			finished: false
		})
    }
}
class TodoList {
	constructor() {
		extendObservable(this, {
			todos: [],
			todoListString: function() {
		        return this.todos.filter(todo => !todo.finished).map((todo, i) => `${i+1}. ${todo.content}`).join('\n');
		    }
		})
	}
}```