<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<input id="jia" type="button" value="+">
<span id="nr">0</span>
<input id="jian" type="button" value="-">
<script>
let jia = document.getElementById('jia');
let jian = document.getElementById('jian');
let nr = document.getElementById('nr');
// 方法一
// jia.onclick = function () {
// nr.innerText++;
// }
// jian.onclick = function () {
// if (nr.innerText > 0) {
// nr.innerText--;
// }
// }
// 方法二
jia.onclick = function () {
nr.innerText++;
jian.onclick = function () {
if (nr.innerText == 0) {
jian.onclick = null;
} else {
nr.innerText--;
}
}
}
</script>
</body>
</html>