how to check if given variable is a collection of html elements?

For example a type of 开发者_如何转开发data that getElementsByClassName or getElementsByTagName produces.

use this code:

var result = document.getElementsByTagName("div");
if (result && result.constructor.name == "NodeList"){
// your code here ;)
} 

or this could be more browser safe

var result = document.getElementsByTagName("div");
if (result && getClassName(result) == "htmlcollection"){
// your code here ;)
}     
function getClassName(obj){
    return ({}).toString.call(obj).match(/\s([a-zA-Z]+)/)[1].toLowerCase();
}

Try this:

function isCollection(input)
{
    return input.item != undefined;
}

But beware any other objects with the method item defined.