JavaScript函数可以有参数的
<!DOCTYPE html>
<html>
<head>
<meta charset = "utf-8">
<title></title>
<script>
function showTips(span_ID,msg){
var span = document.getElementById("span_ID");
span.innerHTML = msg;
}
function checkUsername(){
var uValue = document.getElementById("username").value;
var span = document.getElementById("span_username");
if(uValue.length < 6){
span.innerHTML = "<font color='red' size='2'>对不起，太短</font>";
}else{
span.innerHTML = "<font color='red' size='2'>恭喜你，可用</font>";
}
</script>
</head>
<body>
<form action = "../首页.html">
用户名：<input type="text" id="username" onfocus="showTips('span_username','用户名长度不能小于6')" onblur="checkUsername()"/><span id="span_username"></span><br />
密码：<input type = "password" id = "password" onfocus="showTips('span_password',密码长度不能小于6)"/><span id="span_password"></span><br /><br />
<form>
</body>
</html>引入外部js文件
<script src = "js文件的路径" type="text/javascript" /></script>加载src标签就不会再加载标签里面的内容了。