How to solve the problem when creating an object prototype?

Question

JavaScript

I create prototypes of the object, but the output is ugly.
Help me please

let Unit = {
constructor: function(type,name,force) {
this.type = type;
this.name = name;
this.force = force;
return this
},
greet: function() {
console.log(this.name[0].toUpperCase() + this.name.slice(1) + " ready!")
}
};

let Infantry = Object.create(Unit);
Infantry.constructor = function(type,name,force,infrantryPosibilities) {
Unit.constructor.apply(this,arguments);
this.infrantryPosibilities = infrantryPosibilities || [];
return this;
};

let romanInfantry = Object.create(Unit).constructor('infantry','Caesar Infantry', 15,[1,5,67]);

console.log(romanInfantry.greet()) 
/* Caesar Infantry ready!
(index):53 undefined */
// должна выдавать строку

console.log(romanInfantry) // constructor {type: "infantry", name: "Caesar Infantry", force: 15}
// должна выдавать объект romanInfantry

Answer 1

console.log(romanInfantry.greet())
/* Caesar Infantry ready!
(index):53 undefined */
// should produce a string

It gives you a string: and then the romanInfantry.greet() function returns undefined , because in it you do not have a return value (return ...) To prevent this line (undefined) you can simply write: romanInfantry.greet ().

console.log(romanInfantry) // constructor {type: "infantry", name: "Caesar Infantry", force: 15}
// should produce a romanInfantry object

This object gives you this object, it's just that this object, apparently, is not what you expect.
By the way, I draw your attention to the fact that in the line
You are using 4 arguments whereas in the Unit prototype object method you only have 3.
That you created your own constructor method in Infanity ,

Infantry.constructor = function(type,name,force,infrantryPosibilities) {
Unit.constructor.apply(this,arguments);
this.infrantryPosibilities = infrantryPosibilities || [];
return this;

did not change the original Unit object .
I recommend that you also do a complete revision of the entire code, as the way you have chosen to create prototypes is highly questionable. It should look something like this (if you don't use the class declaration syntax):

// создаёте конструктор класса Unit
function Unit(type,name,force) {
    this.type = type;
    this.name = name;
    this.force = force;
}

// создаёте наследуемые свойства/методы Unit
Unit.prototype = {
    constructor: Unit,
    greet: function() {
        console.log(this.name[0].toUpperCase() + this.name.slice(1) + " ready!")
    }
};
    
// создаёте конструктор класса Infantry
function Infantry(type,name,force,infrantryPosibilities) {
    Unit.call(this,type,name,force);
    this.infrantryPosibilities = infrantryPosibilities || [];
}

// наследуете Infantry класс Unit и замещаете родительское свойство constructor, на новое
Infantry.prototype = Object.create(Unit.prototype, {
    constructor: {
        value: Infantry,
        enumerable: true,
        writable: true,
        configurable: true
    }
});

// создаёте новый экземпляр класса Infantry, наследника Unit.
let romanInfantry = new Infantry('infantry','Caesar Infantry', 15,[1,5,67]);

romanInfantry.greet();
console.log(romanInfantry);