<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
input{
color: #999;
}
</style>
</head>
<body>
<input type="text" value="手机">
<script>
//获取元素 程序处理
var input = document.querySelector(‘input‘);
input.onfocus = function(){
if(this.value == "手机"){
this.value = "";
}
//获得焦点时 让文本框中的值变成黑色
this.style.color = "#333";
}
input.onblur = function(){
if(this.value == ""){
this.value = "手机";
}
//失去焦点时 让文本框中的值变成浅色
this.style.color = "#999";
}
</script>
</body>
</html>
原文：https://www.cnblogs.com/wuyuchuan/p/14772550.html