简单计算器

<!DOCTYPE html>

<html lang="zh-CN">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
</head>
<body>
<fieldset onload="init()">
<legend>小小计算器</legend>
<input type="number" name="n1" id="n1" value="0" oninput="calcu()" />
<select name="" id="opt" oninput="calcu()">
<option value="+">+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
</select>
<input type="number" name="n2" id="n2" value="0" oninput="calcu()" />
<span>=</span>
<span class="res">0</span>
</fieldset>
<script>
const n1 = document.querySelector(“#n1”);
const n2 = document.querySelector(“#n2”);
const opt = document.querySelector(“#opt”);

  function init() {
    n1.value = 0;
    n2.value = 0;
    opt.value = "+";
  }
  function calcu() {
    let value1 = n1.value * 1;
    let value2 = n2.value * 1;
    let optType = opt.value;
    let res = 0;
    switch (optType) {
      case "+":
        res = value1 + value2;
        break;
      case "-":
        res = value1 - value2;
        break;
      case "*":
        res = value1 * value2;
        break;
      case "/":
        if (value2 === 0) throw "除数不能为零";
        res = (value1 / value2).toFixed(2);
        break;
      default:
        throw "非法操作";
    }
    document.querySelector(".res").textContent = res;
  }
</script>

</body>
</html>

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