I kinda like this syntax a lot more than the class syntax

react_stuff.js

var todos = ["Learn React", "Make a Cool Thing", "Retire Early"];

// This is our top-level Component, we render this
const TodosComponent = props => {
  const Todos = renderTodos(props.todos);
  
  return (
    <ul>
      { Todos }
    </ul>
  );
};

// this is a mapping function that takes a list
// and applied a render function over each item
const renderTodos = todos => (
  todos.map(todo => renderTodo(todo))
);

// simply take a single item and render it
const renderTodo = todo => (
  <li>{todo}</li>
);

// Apply our top-level component with its props
// and attach to an existing DOM node
ReactDOM.render(
  <TodosComponent todos={todos} />,
  document.getElementById('container')
)