calculate.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
    if (this.currentOperand.length <= 18){
      this.currentOperand = this.currentOperand.toString() + number.toString()
    }else {
      return
    }
    
    
  }

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

  compute() {
    let computation
    const prev = parseFloat(this.previousOperand)
    const current = parseFloat(this.currentOperand)
    if (isNaN(current)) {
      return
    }else{
      switch (this.operation) {
        case '+':
          computation = prev + current
          break;
        case '-':
          computation = prev - current
          break;
        case '*':
          computation = prev * current
          break;
        case '÷':
          computation = prev / current
          break;
        case '!':
          computation = this.factorial(current)
          break
        case 'mod':
          computation = prev % current
          break;
        default:
          return
      }
    }

    this.currentOperand = computation
    this.operation = undefined
    this.previousOperand = ''
  }
  factorial(n) {
    let result = 1;
    if (n>=0) {
      for (let i=n ; i>=1; --i) {
        result *= i;
      }                    
    }
    return result
    
  }

  updateDisplay() {
    this.currentOperandTextElement.innerText = this.currentOperand
    this.previousOperandTextElement.innerText = this.previousOperand
  }
}

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', () => {
  calculator.compute()
  calculator.updateDisplay()
})

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

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