Understanding this keyword in JS

this.js

const myObject = {
  a: 'b',
  b: 'c',
  doStuff: function() {
    // Here, this refers to myObject
    console.log(this.a + this.b);
  }
}

myObject.doStuff(); // bc

// BUT:
const anotherObject = {
  a: 'abacaba',
  b: '!'
};
anotherObject.doStuff = myObject.doStuff;
anotherObject.doStuff(); // abacaba!

// Arrow functions do not have their own this and refer to the outer one:
const arrowObject = {
  a: 'b',
  // here, this refers to the root function (file itself), which has no idea about a
  doMoreStuff: () => console.log(this.a)
};

arrowObject.doMoreStuff(); // undefined