<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head> <title>DOM event事件</title></head><body><!--1.ondblcilck--><!--<p ondblclick="alert(111)">11</p>--><!--onfocus 获得焦点--><input type="text" onfocus="f1()" onblur="f2()" value="please input your name" class="key_word"><script>function f1() { var ke=document.getElementsByClassName('key_word'); ke[0].value=null;}function f2() { var ke=document.getElementsByClassName('key_word'); if (ke[0].value.trim().length==0){//如果没有输入或者输入空格 ke[0].value="please input your name"; }}</script></body></html>
来源：https://www.cnblogs.com/startl/p/12249709.html