this-keyword-example.js

this-keyword-example.js

var a = 'global';
  
  var check = {
    a: 'hello',
    b: function() {
      console.log(this.a);
    },
    c: function() {
      setTimeout(function(){
        // this becomes global because setTimeout's call site is global
        // as setTimout is window.setTimeout
        console.log(this.a)
      }, 0)
    },
    d: function() {
      // we can reassign this to _this
      var _this = this;
      setTimeout(function() {
        console.log(_this.a)
      })
    },
    e: function() {
      // Arrow function brings lexical scope
      setTimeout(() => {
        console.log(this.a)
      })
    }
  }

  check.b();
  check.c();
  check.d();
  check.e();