Why does a method's `this` change when calling a reference to an object's method?

Question

function Person(gender) {
  this.gender = gender;
}

Person.prototype.sayGender = function()
{
  alert(this.gender);
};

var person1 = new Person(\'Male\');
var gend         


        

Answer 1

You are calling the function without the context of its object, so this will be the global object window, so the function alerts the value of window.gender, which is undefined.