text: class Person {
    constructor(firstName, lastName) {
      this.firstName = firstName
      this.lastName = lastName
    }
  
    sayHi1() {
      console.log(`Hi, my name is ${this.firstName}!`)
    }
  
    sayHi2 = () => {
      console.log(`Hi, my name is ${this.firstName}!`)
    }
  }
  
  const p = new Person('f', 'l')
  p.sayHi1()
  // Hi, my name is f!
  
  // methods in class are implicitly in strict mode
  const greet1 = p.sayHi1
  greet1() // TypeError: Cannot read property 'firstName' of undefined...
  
  const greet2 = p.sayHi2
  greet2() // Hi, my name is f!
  