“¿Por qué esto está indefinido en React?” Código de respuesta

¿Por qué esto está indefinido en React?

There are a couple of ways to deal with it. see first stackoverflow answer you
will get it.

One is to add this.onToggleLoop = this.onToggleLoop.bind(this); in the constructor.

Another is arrow functions onToggleLoop = (event) => {...}.

And then there is onClick={this.onToggleLoop.bind(this)}.