代碼如下：
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title>js計算器</title>
<script>
function calculator(){
var num1 = parseFloat(document.getElementById("num1").value);
var num2 = parseFloat(document.getElementById("num2").value);
var result = parseFloat(document.getElementById("result").value);
var mark = document.getElementById("mark").value;
switch (mark){
case "+" :
result = num1 + num2;
break;
case "-" :
result = num1 - num2;
break;
case "*" :
result = num1 * num2;
break;
case "/" :
result = num1 / num2;
break;
}
document.getElementById("result").value = result;
}
</script>
</head>
<body>
<input type="number" id="num1" >
<select id="mark">
<option> + </option>
<option> - </option>
<option> * </option>
<option> / </option>
</select>
<input type="number" id="num2" >
<button onclick="calculat0r()"> = </button>
<input type="text" id="result" >
</body>
</html>
效果如下：
