(JavaScript) THIS Keyword

 

'use strict';

 

console.log(this); // Window Object

 

const calcAge = function (birthYear) {

  console.log(2037 - birthYear);

  console.log(this);

};

 

calcAge(1991); // undefined

 

const calcAgeArrow = birthYear => {

  // it doesn't have a this keyword

  console.log(2037 - birthYear);

  console.log(this);

};

 

calcAgeArrow(1988); // window

 

const hongsik = {

  year: 1988,

  calcAge: function () {

    console.log(this);

    console.log(2037 - this.year);

 

    function calcAge2() {

      console.log(this);

    }

 

    calcAge2(); // Undeifiend

  },

};

 

hongsik.calcAge();

 

const matilda = {

  year: 2017,

};

 

matilda.calcAge = hongsik.calcAge; // Method borrowing

matilda.calcAge();

 

const f = hongsik.calcAge;

// f(); // error - doesnt have year variable