<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>labels</title>
</head>
<body>
<script>
function Validate() {
var txtName = document.getElementById("txt_name");
var button = document.getElementById("btn");
var form = document.getElementById("testform");
if (txtName.value.trim() == "") {
var label = document.createElement("label");
label.setAttribute("for","txt_name");
form.insertBefore(label,button);
txtName.labels[1].innerHTML = "please input your name!";
txtName.labels[1].setAttribute("style", "font-size:9px;color:red");
}
}
</script>
<form id="testform">
<label for="txt_name"> name:</label>
<input id="txt_name">
<input type="button" id="btn" value="验证" onclick="Validate()">
</form>
</body>
</html>效果图：
点击后：