Arrow functions is not a syntax sugar for functions

arrow.js

const withFunction = {
  myOwnProp: 42,
  myOwnFunc: function () {
    return this.myOwnProp
  }
}

const withArrow = {
  myOwnProp: 42,
  myOwnFunc: () => {
    return this.myOwnProp
  }
}

console.log(withFunction.myOwnFunc()) // 42
console.log(withArrow.myOwnFunc())    // undefined