JavaScript中访问节点对象的方法有哪些如何使用

JavaScript中访问节点对象的方法有哪些？

var obj = document.getElementById('fdafda'); var obj = document.f1; 
obj.method="post"; 
obj.action='Bb'; 
var obj = document.f1.userName; 
var obj = document.forms[0].userName; 
var obj = document.forms[0].elements[0]; 
var obj = document.f1.elements[0]; 
var obj = document.forms["f1"].elements["userName"]; 
var obj = document.forms[0].like; 
for(var i=0;i<obj.length;i++) 
{ 
var aa = obj[i]; 
if(aa.checked) 
{ 
alert(); 
} 
} 
<form name="f1" action="AA"> 
<input type="text" name="userName" id="userName"/> 
<input type="checkbox" name="like" value="sport"/> 
<input type="checkbox" name="like" value="art"/> 
<input type="checkbox" name="like" value="music"/> 
</form> 
<form name="f1" action="AA"> 
<input type="text" name="userName" id="userName"/> 
<input type="checkbox" name="like" value="sport"/> 
<input type="checkbox" name="like" value="art"/> 
<input type="checkbox" name="like" value="music"/> 
</form> 
<form name="f1" action="AA"> 
<input type="text" name="userName" id="userName"/> 
<input type="checkbox" name="like" value="sport"/> 
<input type="checkbox" name="like" value="art"/> 
<input type="checkbox" name="like" value="music"/> 
</form>