Найти алгоритм для нахождения суммы определенных елементов статического массива и их соответсвия заданому числу?

очень благодарен Вам!

Как создать свой собственный метод?

прошу извинить за мою наглость, но Вы могли бы расписать пример полностью, я в прототипах слабо розбираюсь, изучаю.

Как применить условие выполнения к методам класса?

оно не работает(
'use strict'

class Tamagotchi {

constructor(name){
this.name = name;
this.health = 100;
}

healthLo() {
this.health -= 20;
}

healthHi() {
this.health += 20;
}

hello() {
console.log('HI! My name is ' + this.name + '! Play with me!');
}

eat() {
let eatHamster = confirm("I want to eat...");
if(eatHamster) {
this.healthHi();
console.log(this.name + " eating now...plus to health 20%! " + "current health value:" + this.health );
} else {
this.healthLo();
console.log('Time to drink...' + "current health value:" + this.health);
}
}

drink() {
let drinkHamster = confirm("I want to drink...");
if(drinkHamster) {
this.healthHi();
console.log(this.name + " drinking now...plus to health 20% " + "current health value:" + this.health );
} else {
this.healthLo();
console.log('Time to sleep...' + "current health value:" + this.health);
}
}

sleep() {
let sleepHamster = confirm("I want to sleep...");
if(sleepHamster) {
this.healthHi();
console.log(this.name + " sleeping now...plus to health 20% " + "current health value:" + this.health );
} else {
this.healthLo();
console.log('Time to play...' + "current health value:" + this.health);
}
}

play() {
let playHamster = confirm("I want to play...");
if(playHamster) {
this.healthHi();
console.log(this.name + " playing now...plus to health 20% " + "current health value:" + this.health );
} else {
this.healthLo();
if(this.health > 20) {
console.log("I like you!" + "current health value:" + this.health);
} else {
console.log("I want to died...help me!" + "current health value:" + this.health);
}
}
}


sick() {
this.healthLo();
console.log('pills dont help!!!' + "current health value:" + this.health);
}

died() {
console.log('Sorry! Your ' + this.name + ' is died!!!' + "current health value:" + this.health);
}

}

let name = prompt('Enter please name: ','name');

let hamster = new Tamagotchi(name);

if (hamster) {
hamster.hello();
}

if (hamster.health > 80 || hamster.health < 100) {
hamster.eat();
}

if (hamster.health > 60 || hamster.health < 80) {
hamster.sleep();
}

if (hamster.health >= 100) {
hamster.play();
}

if (hamster.health > 40 || hamster.health < 60) {
hamster.drink();
}

if (hamster.health > 20 || hamster.health < 40) {
hamster.sick();
}

if (hamster.health < 20) {
hamster.died();
}