<!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 Txt1 = document.getElementById('txt1');
var Txt2 = document.getElementById('txt2');
var oAdd = document.getElementById('add');
oAdd.onclick = function() {
/* float number更嚴格 NaN不是數字*/
var num1 = Number(Txt1.value);
var num2 = Number(Txt2.value);
alert(num1 + num2)
}
}
</script>
</head>
<body>
<input type="text" id="txt1">+
<input type="text" id="txt2">
<input type="button" value="總和" id="add">
</body>
</html>
