Where does it get the new array element from and where does it put the values?

Question

Node.js

I decided to do a friend's task, in a language convenient for myself, and so as not to once again call the survey from the console, I decided to do it through the discord.
The task was like this:

Enter n integers(>0 or <0). Find the difference of numbers. Display the result on the screen.

I wrote code for this:

const Discord = require('discord.js');
const bot = new Discord.Client();
const {token1} = require('./conf.json');
var mas =[]
var prom =[]
let a
let i=1

bot.on("message", msg => {
    msg.content = msg.content.toLowerCase().split(" ")
    switch (msg.content[0]) {
        case"!add":
            if (!msg.author.bot){
                if (!msg.content[2]) {
                    msg.reply("Введите, хотя бы 2 значения!")
                } else {
                    mas=[]
                    for (let i = 1; msg.content[i]; i++) {
                        mas.push(Number(msg.content[i]))
                    }
                    msg.reply("Готово. Можете вводить !math")
                    a = mas.length + 1
                }
            }
        break;
        case"!math":
            try{
                prom = []
                mas.push(0)
                while(i<mas.length){
                    mas[a] = mas[i-1] - mas[i];
                    prom.push(mas[a])
                    i++
                }
                console.log(mas)
                console.log(prom)
                msg.reply("Результат: " + mas[a-1] + "\nПромежуточные результаты: " + prom)
                mas = []
            }catch (e) {
                msg.reply("Сначала введите значения!!!")
            }
        break;
    }
})

bot.login(token1);

But instead of working normally, it decides to prove itself:



1) It did not write the intermediate result to prom
2) It took another array element from somewhere and refused to count
3) It simply refused to count

I want to understand by what principle this additional element arises and in general how cleanly this task is performed.
Thanks in advance!

Answer 1

bot.on("message", msg => {

  let [type, ...data] = msg.content.toLowerCase().split(" ");

  if (msg.author.bot) return; // игнорируем бота

  switch (type) {
    case "!add":
      if (data.length < 2) return msg.reply("Введите, хотя бы 2 значения!");

      if (data.find(e => isNaN(e) || Number(e) === 0 || Math.floor(e) !== Number(e))) {
        return msg.reply("Числа должны быть целыми в диапазоне (-∞, 0), (0, ∞)");
      }

      msg.reply("Результат: " + data.slice(1).reduce((acc, cur, index) => acc - cur, data[0]));
      break;

    default:
      msg.reply("Чтобы вычислить разницу чисел. Вызовите команду !add <числа через пробел>");
      break;
  }

})

For the task at hand, your code is too confusing. You don’t need to save intermediate results anywhere, and you don’t need to ask the user to enter ! math

Answer 2

let msg = "!add 45 15 30"

let prom = [];
let result = 0;


let message = msg.toLowerCase().split(" ");

if(message[0] == "!add") {
    prom = [];
    result = 0;
    
    if(message.length < 3) {
        console.log('Введите хотя бы 2 значения!');
    }
    else {
        for(let i=1; i<message.length; i++) {
            result += Number(message[i])
            prom.push(result)
        }
        console.log('Готово! Можете вводить !math')
        console.log(prom)
        console.log(result)
    }
}
if(message[0] == "!math") {
    console.log(prom)
    console.log(result)
}

adjust for yourself