How to create a JavaScript Calculator Using HTML, CSS, and JavaScript

				
					let lastInput = ''; // Tracks the last input to avoid consecutive operators
let expression = ''; // Stores the current calculation expression
let resultShown = false; // Tracks whether result is shown to allow further calculations

function appendNumber(number) {
  const display = document.getElementById('display');
  
  if (resultShown) {
    expression = ''; // Reset expression if result is shown
    resultShown = false;
  }
  
  // Append number to the expression and display it
  expression += number;
  display.value = expression;
  
  lastInput = number;
}

function appendOperator(operator) {
  const display = document.getElementById('display');
  
  // Prevent adding operator at the start or consecutively
  if (expression === '' || isOperator(lastInput)) {
    return;
  }
  
  expression += operator;
  display.value = expression;
  
  lastInput = operator;
  resultShown = false; // Continue calculations after an operator
}

function clearDisplay() {
  document.getElementById('display').value = '';
  document.getElementById('result-display').innerHTML = '';
  expression = '';
  lastInput = '';
}

function deleteDigit() {
  expression = expression.slice(0, -1); // Remove last character
  document.getElementById('display').value = expression;
  
  lastInput = expression.slice(-1); // Update lastInput
}

function calculateResult() {
  const display = document.getElementById('display');
  const resultDisplay = document.getElementById('result-display');
  
  try {
    if (expression && !isOperator(lastInput)) {
      const result = eval(expression); // Calculate result
      resultDisplay.innerHTML = `${expression} = ${result}`; // Show result on top
      display.value = result; // Show result in main display
      expression = result.toString(); // Store the result for further calculations
      resultShown = true;
    }
  } catch {
    display.value = 'Error';
  }
}

function isOperator(char) {
  return ['+', '-', '×', '/'].includes(char);
}