关于Promise中this的指向问题？

class Dog {

  constructor() {

    this.name = 'adong';

  }



  start() {

    this.p().then(this.say);

  }



  p() {

    return new Promise((resolve, reject)=>{

      resolve('good');

    })

  }

 

  say(str) {

    console.log(this);

    console.log(this.name + str);

  }

}



let dog = new Dog();

dog.start();