script.js

let display = document.querySelector('.display')
let firstNum = 0
let secondNum = 0
let selectedOperator = ''
let resetSwitch = false

let add = document.querySelector('.add')
let subtract = document.querySelector('.subtract')
let multiply = document.querySelector('.multiply')
let divide = document.querySelector('.divide')

display.textContent = firstNum

function updateDisplay(input){
    // remove leading zeros
    display.textContent += input
    if (Array.from(display.textContent)[0] == ('0' || 0)) {
        display.textContent = display.textContent.slice(1)
    }
}

function clearFunc(){
    display.textContent = 0
    firstNum = 0
    secondNum = 0
    selectedOperator = ''
}

function resetDisplay() {
    display.textContent = 0
    resetSwitch = false
}

let numbers = document.querySelectorAll('.num')

numbers.forEach(item => {
    item.addEventListener('click', () => {
        if (resetSwitch) {
            if (selectedOperator.length > 1) {
                resetDisplay()
            }
        }
        updateDisplay(item.textContent)
    })
})


let clear = document.querySelector('.clear')

clear.addEventListener('click', () => {
    clearFunc('')
})

function loadFirstNum() {
    firstNum = display.textContent
}

function addFunc(){
    loadFirstNum()
    selectedOperator = 'add'
    resetSwitch = true
}
function subtractFunc(){
    loadFirstNum()
    selectedOperator = 'subtract'
    resetSwitch = true
}
function multiplyFunc(){
    loadFirstNum()
    selectedOperator = 'multiply'
    resetSwitch = true
}
function divideFunc(){
    loadFirstNum()
    selectedOperator = 'divide'
    resetSwitch = true
}

add.addEventListener('click', addFunc)
subtract.addEventListener('click', subtractFunc)
multiply.addEventListener('click', multiplyFunc)
divide.addEventListener('click', divideFunc)

function total(a,b) {
    if (selectedOperator == 'add') {
        return (+a + +b).toFixed(2)
    } else if (selectedOperator == 'subtract') {
        return (+a - +b).toFixed(2)
    } else if (selectedOperator == 'multiply') {
        return (+a * +b).toFixed(2)
    } else if (selectedOperator == 'divide') {
        return (+a / +b).toFixed(2)
    }
}

function isWhole(n) {
   var result = (n - Math.floor(n)) !== 0; 
   
  if (result)
    return false;
   else
    return true;
}

function loadSecondNum() {
    secondNum = display.textContent
    newNum = total(firstNum,secondNum)

    if (isWhole(newNum)) {
        newNum = Math.trunc(newNum)
        display.textContent = newNum
    } else {
        display.textContent = newNum
    }
}

let equals = document.querySelector(".equals")

equals.addEventListener('click', loadSecondNum)