SOURCE

class Ml {
  constructor(opt) {
    this.name = opt.name || 'name';
    this.key = opt.key || 'key';
  }
  init = () => {
    this.name = 'init name';
    this.age = 20;
  }
}
let ml = new Ml({
  name: 'kklll'
});
console.log(ml.name);
ml.init();
console.log(ml.name,ml.age);