eltonvs/web01_ex01.html

## web01_ex01.html
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>JS Expression Calculator</title>
</head>
<body>
  <h1>Expression Calculator</h1>
  Enter the expression:
  <input id="expression" type="text" name="expression">
  <button id="calculate-expr" type="submit">Calculate</button>
  <div class="result-area">
    Result: <strong id="expr-result">empty expression</strong>
  </div>

  <script>
    let btn_calculate = document.getElementById('calculate-expr')
    let expression = document.getElementById('expression')
    let result_element = document.getElementById('expr-result')
    let expression_pattern = /[0-9\(\)\-\/\*.\+\ ]+/

    btn_calculate.addEventListener('click', e => {
      let expr_raw = expression.value.trim()

      if (expression_pattern.test(expr_raw)) {
        expr_result = eval(expr_raw)
      }

      result_element.textContent = typeof expr_result === 'number' ?
        expr_result : "Error processing expression"
    })
  </script>
</body>
</html>
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<title>JS Expression Calculator</title>
	</head>
	<body>
	<h1>Expression Calculator</h1>
	Enter the expression:
	<input id="expression" type="text" name="expression">
	<button id="calculate-expr" type="submit">Calculate</button>
	<div class="result-area">
	Result: <strong id="expr-result">empty expression</strong>
	</div>

	<script>
	let btn_calculate = document.getElementById('calculate-expr')
	let expression = document.getElementById('expression')
	let result_element = document.getElementById('expr-result')
	let expression_pattern = /[0-9\(\)\-\/\*.\+\ ]+/

	btn_calculate.addEventListener('click', e => {
	let expr_raw = expression.value.trim()

	if (expression_pattern.test(expr_raw)) {
	expr_result = eval(expr_raw)
	}

	result_element.textContent = typeof expr_result === 'number' ?
	expr_result : "Error processing expression"
	})
	</script>
	</body>
	</html>