scope.js

function A (name) {
  this.name = name;
  this.sayMyName = this.sayMyName.bind(this);
}

A.prototype = {
  sayMyName: () => {
    console.log(this.name); // -> undefined
  }
};

function B (name) {
  this.name = name;
  this.sayMyName = this.sayMyName.bind(this);
}

B.prototype = {
  sayMyName: function() {
    console.log(this.name);
  }
};

let test = {
  a: new A("a"),
  b: new B("b"),
}

test.a.sayMyName();
test.b.sayMyName();