How do I wrap a function with an object in a class in javascript?

Question

Let's say I have a class named Human.

function Human(name, gender, age, personality){
    this.name = name;
    this.gender = gender;
    this.age = age;
    this.personality = personality; 
}

and I have some functions for the class such as greeting and introduce. So I create them like this:

Human.prototype.introduce = function() {
    var _gender = {"M": "Boy", "F": "Girl"};
    switch(this.personality)
    {
    case "passionate":
        alert("Hi, how are you? My name is " + this.name + ". I'm " + this.age + " years old " + _gender[this.gender] + ". ");
        break;
    case "aggressive":
        alert("I'm " + this.name + ". What you want? ");
        break;
    }
}

Human.prototype.greeting = function() {
    alert("Hi!");
}

Since introduce and greeting can be grouped by the same category (let's name it speak), how can I simply wrap this two functions with an object? I've tried this:

Human.prototype.speak = {};
Human.prototype.speak.greeting = function(){
    alert("Hi!");
}
Human.prototype.speak.introduce = function(){
var _gender = {"M": "Boy", "F": "Girl"};
        switch(this.personality)
        {
        case "passionate":
            alert("Hi, how are you? My name is " + this.name + ". I'm " + this.age + " years old " + _gender[this.gender] + ". ");
            break;
        case "aggressive":
            alert("I'm " + this.name + ". What you want? ");
            break;
        }
}

Now the question is, when a function is wrapped by an object, this in the introduce function is no longer referring to the instance. So how can I work this out?

I would like to call the function as this:

var eminem = new Human("Marshall Mathers", "M", 45, "aggressive");
eminem.speak.introduce();

Answer 1

Make Speak to A Class

Make Speak to a class, because logical grouping of variables and functionality in OOP are classes.

Speak

function Speak(human) {
    this.human = human
}

Speak.prototype.greeting = function () {
    // ...
}

Speak.prototype.introduce = function () {
    // ..
}

Human

function Human(name, gender, age, personality, greetWord) {
    this.name = name;
    this.gender = gender;
    this.age = age;
    this.personality = personality;
    this.speak  = new Speak(this)
}

Example

function Human(name, gender, age, personality, greetWord) {
    this.name = name;
    this.gender = gender;
    this.age = age;
    this.personality = personality;
    this.greetWord = greetWord;
    this.speak  = new Speak(this)
}

function Speak(human) {
    this.human = human
}

Speak.prototype.greeting = function () {
    alert(this.human.greetWord + "!");
}

Speak.prototype.introduce = function () {
    var _gender = { "M": "Boy", "F": "Girl" };
    switch (this.human.personality) {
        case "passionate":
            alert("Hi, how are you? My name is " + this.human.name + ". I'm " + this.human.age + " years old " + _gender[this.human.gender] + ". ");
            break;
        case "aggressive":
            alert("I'm " + this.human.name + ". What you want? ");
            break;
    }
}

var peter = new Human('Peter', 'M', 35, 'aggressive', 'Hi')
peter.speak.greeting()
peter.speak.introduce()

---

An other way to solve the solution would be to use apply.

Apply

The apply() method calls a function with a given this value, and arguments provided as an array (or an array-like object).

Code

var peter = new Human('Peter', 'M', 35, 'aggressive')
console.log(peter.speak.introduce.apply(peter))

Example

function Human(name, gender, age, personality){
    this.name = name;
    this.gender = gender;
    this.age = age;
    this.personality = personality; 
}

Human.prototype.speak = {};
Human.prototype.speak.greeting = function(){
    alert("Hi!");
}
Human.prototype.speak.introduce = function(){
var _gender = {"M": "Boy", "F": "Girl"};
        switch(this.personality)
        {
        case "passionate":
            alert("Hi, how are you? My name is " + this.name + ". I'm " + this.age + " years old " + _gender[this.gender] + ". ");
            break;
        case "aggressive":
            alert("I'm " + this.name + ". What you want? ");
            break;
        }
}

var peter = new Human('Peter', 'M', 35, 'aggressive')
console.log(peter.speak.introduce.apply(peter))