通过输入框输入内容，简单的计算得到结果
image.png
<body>
<p>
<input type="text" id="num1" />+<input type="text" id="num2" />=
<span id="result"></span>
</p>
<p>
<button onclick="compute()">计算</button>
</p>
<script>
function compute() {
var num1 = document.getElementById("num1").value;
var num2 = document.getElementById("num2").value;
var $span = document.getElementById("result");
if (num1 == "" && num2 == "") {
alert("请输入数值");
} else {
var sum = num1 * 1 + num2 * 1;
$span.innerText = sum;
}
}
</script>
</body>