js动态实现密码输入框与文本输入框的切换

/* 密码输入框 */ var tx = document.getElementById("tx"), pwd = document    .getElementById("pwd");  tx.onfocus = function() {   if (this.value != "请输入密码"){    return;    }else{   this.select();   

    }  }  tx.onclick=function(){         this.style.display = "none";   pwd.style.display = "";   pwd.value = "";   pwd.focus();   }  pwd.onblur = function() {   if (this.value != "")    return;   this.style.display = "none";   tx.style.display = "";   tx.value = "请输入密码";  }

 if (!!window.attachEvent && navigator.userAgent.match(/msie (\d)/i)[1] > 8){   document.attachEvent("onkeydown", function() {    var key ;    if(window.event) // IE       {       key = event.keyCode       }      else if(event.which) // Netscape/Firefox/Opera       {       key = event.which       }        if (key == 8) {     if (pwd.value.length <= 1) {      pwd.style.display = "none";      tx.style.display = "";      tx.value = "请输入密码";      var elem = window.event.srcElement;      var name = elem.nodeName;      if (name != 'INPUT') {       event.returnValue = false;       return;      }      var type_e = elem.type.toUpperCase();      if (name == 'INPUT') {       event.returnValue = false;       return;      }     } else {              return;     }    }else{           return;    }           });  }

 <input id="tx" name="" type="text" value="请输入密码"   onMouseOver="this.onfocus()" onMouseOut="if(this.value=='')this.value='请输入密码';"  />
      <input id="pwd"name="" type="password" style="display: none"/>