<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
window.onload = function() {
var oNum1 = document.getElementById('num1');
var oNum2 = document.getElementById('num2');
var oBtn = document.getElementById('btn');
var oS = document.getElementById('sele');
oBtn.onclick = function() {
var iNum1 = parseFloat(oNum1.value);
var iNum2 = parseFloat(oNum2.value);
switch (oS.value) {
case '+':
console.log(iNum1 + iNum2);
break;
case '-':
console.log(iNum1 - iNum2);
break;
case 'x':
console.log(iNum1 * iNum2);
break;
case '/':
console.log(iNum1 / iNum2);
break;
}
}
}
</script>
</head>
<body>
<input type="text" id="num1">
<select name="" id="sele">
<option value="+">+</option>
<option value="-">-</option>
<option value="x">x</option>
<option value="/">/</option>
</select>
<input type="text" id="num2">
<input type="button" value="計算" id="btn">
</body>
</html>
運行結果
