<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>无标题文档</title>
<script>
window.onload = function (){
var aInp = document.getElementsByTagName(‘input‘);
var str = ‘‘;
aInp[1].onclick = function (){
str = aInp[0].value;
// HTML 中拿到的内容，类型都是字符串
// alert( typeof str );
if( isNaN(str) ){
alert( str + ‘不是数字‘ );
}else{
alert( str + ‘是数字‘ );
}
};
};
</script>
</head>
<body>
<input type="text" />
<input type="button" value="判断输入值是不是数字" />
</body>
</html>
原文：https://www.cnblogs.com/tongguilin/p/12208128.html