<title>JavaScript给按钮加上双重动作</title>
<script language=JavaScript>
function jdk1x() {
  var num1 = document.x.jdk.value;
  if(num1 == 'three') {
  document.x.jdk.value = document.x.jdk.value
    }
  else {
  document.x.jdk.value = "欢迎您！"
    }
location="https://www.jb51.net/"
 }
 </script>
<form name=x>
<input type=button value="" onClick="jdk1x()"><br>
<input type=text name=jdk width="300" onChange="document.x.jdk.value=''; return true">
</form>