SOURCE

var name = 'window'
  var person1 = {
    name: 'person1',
    foo1: function() {
      console.log(this.name)
    },
    foo2: () => {
      console.log(this.name)
    },
    foo3() {
      return function() {
        console.log(this.name)
      }
    },
    foo4() {
      return () => {
        console.log(this.name)
      }
    }
  }

  var person2 = { name: 'person2' }

  person1.foo1()// person1
  person1.foo1.call(person2) // person2

  person1.foo2() // 'window'
  person1.foo2.call(person2) // ‘window’

  person1.foo3()() // 'window'
  person1.foo3.call(person2)() // 'window'
  person1.foo3().call(person2) // person2

  person1.foo4()() // person1
  person1.foo4.call(person2)() // person2
  person1.foo4().call(person2) // person1