20150619验证用户是否输入

html=============

user:<input id=‘user‘ type="text">
password:<input id=‘password‘ type="text">        
<input id=‘button‘ type="button" value="check">

js===============

var user=document.getElementById(‘user‘);
var password=document.getElementById(‘password‘);
var button=document.getElementById(‘button‘);
button.onclick=function () {
    if(user.value.length<=0){
        alert(‘no user‘);
    }else if(password.value.length<=0){
        alert(‘no password‘);
    }else{
        alert(‘ok‘);
    }
}