index.js

// Creating Calculator class

class Calculator {
  constructor(previousDisplay, currentDisplay) {
    this.previousDisplay = previousDisplay;
    this.currentDisplay = currentDisplay;
    this.allClear();
  }

  allClear() {
    this.currentOperand = "";
    this.previousOperand = "";
    this.operation = "";
  }
  delete() {
    this.currentOperand = this.currentOperand.toString().slice(0, -1);
  }

  equals() {}
  divide() {}
  multiply() {}
  subtract() {}
  add() {}

  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 curr = parseFloat(this.currentOperand);
    if (isNaN(prev) || isNaN(curr)) return;
    switch (this.operation) {
      case "+":
        computation = prev + curr;
        break;
      case "−":
        computation = prev - curr;
        break;
      case "×":
        computation = prev * curr;
        break;
      case "÷":
        computation = prev / curr;
        break;
      default:
        return;
    }
    this.currentOperand = computation;
    this.previousOperand = "";
    this.operation = undefined;
  }

  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.currentDisplay.innerText = this.getDisplayNumber(this.currentOperand);
    if (this.operation != null) {
      this.previousDisplay.innerText = `${this.getDisplayNumber(
        this.previousOperand
      )} ${this.operation}`;
    } else
      this.previousDisplay.innerText = this.getDisplayNumber(
        this.previousOperand
      );
  }
}

const numberButton = document.querySelectorAll("[data-number]");
const operationButton = document.querySelectorAll("[data-operation]");
const equalsButton = document.querySelector("[data-equals]");
const deleteButton = document.querySelector("[data-delete]");
const allClearButton = document.querySelector("[data-all-clear]");
const previousDisplay = document.querySelector("[data-previous]");
const currentDisplay = document.querySelector("[data-current]");

// Creating calculator object

const calculator = new Calculator(previousDisplay, currentDisplay);

// Defining all the events

numberButton.forEach((button) => {
  button.addEventListener("click", () => {
    calculator.appendNumber(button.innerText);
    calculator.updateDisplay();
  });
});

operationButton.forEach((button) => {
  button.addEventListener("click", () => {
    calculator.chooseOperation(button.innerText);
    calculator.updateDisplay();
  });
});

allClearButton.addEventListener("click", () => {
  calculator.allClear();
  calculator.updateDisplay();
});

equalsButton.addEventListener("click", () => {
  calculator.compute();
  calculator.updateDisplay();
});

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