script.js

class Calculator {
    constructor(previousOperandTextElement, currentOperandTextElement){
        this.previousOperandTextElement = previousOperandTextElement
        this.currentOperandTextElement = currentOperandTextElement
        this.clear();
    }

    clear() {
        this.currentOperand = ''
        this.previousOperand = ''
        this.operation = undefined;

    }

    delete(){
        this.currentOperand = this.currentOperand.toString().slice(0, -1)

    }


    appendNumber(number){
        if(number === '.' && this.currentOperand.includes('.')) return
        this.currentOperand = this.currentOperand.toString() + number.toString();
    }

    chooseOperation(operation){
        if(this.currentOperand === '') return
        if(this.previousOperand !== '') {
            this.compute()
        }
        this.operation = operation
        this.previousOperand = this.currentOperand
        this.currentOperand = ''
    }

    compute(){
        let computation
        const prev = parseFloat(this.previousOperand)
        const current = parseFloat(this.currentOperand)
        if (isNaN(prev) || isNaN(current)) return
        switch (this.operation){
            case '+':
                computation = prev + current
                break
            case '-':
                computation = prev - current
                break
            case '*':
                computation = prev * current
                break
            case '÷':
                computation = prev / current
                break
            default:
                return
        }
        this.currentOperand = computation
        this.operation = undefined
        this.previousOperand = ''
    }

    getDisplayNumber(number){

        const stringNumber = number.toString()
        const integerDigits = parseFloat(stringNumber.split('.')[0])
        const decimalDigits = stringNumber.split('.')[1]
        let integerDisplay
        if(isNaN(integerDigits)) {
            integerDisplay = ''
        } else {
            integerDisplay = integerDigits.toLocaleString('en', {maximumFractionDigits: 0})
            }
        if (decimalDigits != null){
            return `${integerDisplay}.${decimalDigits}`
        } else {
            return integerDisplay
        }

    }

    updateDisplay(){

        this.currentOperandTextElement.innerText = this.getDisplayNumber(this.currentOperand)
        if (this.operation != null ) {
        this.previousOperandTextElement.innerText =
         `${this.getDisplayNumber(this.previousOperand)}${this.operation}`
        } else {
             this.previousOperandTextElement.innerText = ''
        }
    }

}


const numberButtons = document.querySelectorAll('[data-number]')
const operationButtons = document.querySelectorAll('[data-operation]')
const equalsButton = document.querySelector('[data-equals]')
const deleteButton = document.querySelector('[data-delete]')
const allClearButton = document.querySelector('[data-all-clear]')
const previousOperandTextElement = document.querySelector('[data-previous-operand]')
const currentOperandTextElement = document.querySelector('[data-current-operand]')

const calculator = new Calculator(previousOperandTextElement, currentOperandTextElement)

numberButtons.forEach(button => {
    button.addEventListener('click', () => {calculator.appendNumber(button.innerText)
    calculator.updateDisplay()
    })
})

operationButtons.forEach(button => {
    button.addEventListener('click', () => {calculator.chooseOperation(button.innerText)
    calculator.updateDisplay()
    })
})

equalsButton.addEventListener('click', button => {
    calculator.compute()
    calculator.updateDisplay()
    })

allClearButton.addEventListener('click', button => {
    calculator.clear()
    calculator.updateDisplay()
    })

deleteButton.addEventListener('click', button => {
    calculator.delete()
    calculator.updateDisplay()
    })