this_in_functions.js

// function form
function fnForm() {
  console.log('function form: ', this);
}

fnForm(); // function form - this is the global object - (window)

// method form
var parent = function parent() {
  var p = {};
  p.methodForm = function methodForm() {
    console.log('method form: ', this);
  };
  
  this.applyForm = function applyForm() {
    console.log('apply form: ', this);
  }
  
  return p;
}

var f = parent();
f.methodForm();

// constructor form
var fn = new fnForm();

// apply/call form
fnForm.call(parent, 1, 2);
fnForm.apply(parent, [1, 2]);