如何在JavaScript中检测HTMLCollection / NodeList？

Question

I'm not sure my current implementation is available all the time:

function isNodeList(nodes) {
    var result = Object.prototype.toString.call(nodes);
    // modern browser such as IE9 / firefox / chrome etc.
    if (result === '[object HTMLCollection]' || result === '[object NodeList]') {
        return true;
    }
    //ie 6/7/8
    if (typeof(nodes) != 'object') {
        return false;
    }
    // detect length and item 
    if (!('length' in nodes) || !('item' in nodes)) {
        return false;
    }
    // use the trick NodeList(index),all browsers support
    try {
        if (nodes(0) === null || (nodes(0) && nodes(0).tagName)) return true;
    }
    catch (e) {
        return false;
    }
    return false;
}

A common situation is {length:1,item:function(){return [];}}
The value of result in chrome / safari / opera is '[object NodeList]'.
In firefox and IE 9 , it is '[object HTMLCollection]'.

Which is the standard value?

Answer 1

The following should return true , if nodes is of type

NodeList.prototype.isPrototypeOf(nodes)

@DavidSpector, for HTMLCollection you can similarly use :

HTMLCollection.prototype.isPrototypeOf(collection)

Answer 2

I would structure the code differently:

function isNodeList(nodes) {
    var stringRepr = Object.prototype.toString.call(nodes);

    return typeof nodes === 'object' &&
        /^\[object (HTMLCollection|NodeList|Object)\]$/.test(stringRepr) &&
        (typeof nodes.length === 'number') &&
        (nodes.length === 0 || (typeof nodes[0] === "object" && nodes[0].nodeType > 0));
}

Notes:

• less return paths make easier-to-read code
• stick with one type of logic, if possible (ie use less negated checks)
• "item" is not mandatorily in a nodeList
• use hasOwnProperty() instead of in
• use square brackets to index into the list
• I don't think a try/catch is really necessary, but that might be wrong - you decide
• check for nodeType instead of tagName , as text nodes or comments do not have a name
• add more checks to the && chain if you see fit

Answer 3

script :

Element.prototype.isNodeList = function() {return false;}
NodeList.prototype.isNodeList = HTMLCollection.prototype.isNodeList = function(){return true;}

use like this :

var d; // HTMLCollection|NodeList|Element
if(d.isNodeList()){
  /*
    it is HTMLCollection or NodeList
    write your code here
  */
}else{
  /*
    it is not HTMLCollection and NodeList
    write your code here
  */
}

Answer 4

Here is how to test if an object is a NodeList in modern browsers:

if (nodes instanceof NodeList) {
  // It's a NodeList object
}

Answer 5

Check if variable is an HTMLcollection or a dom element

  var foo = document.getElementById('mydiv');
  var foo2 = document.getElementsByClassName('divCollection');
  console.log(foo instanceof HTMLElement);
  console.log(foo instanceof HTMLCollection);

Answer 6

This answer is probably really really late, but....

if (nodes == '[object NodeList]') {
  // It's a nodeList
}

Answer 7

I created a benchmark of all answers here to see, what is the best approve in speed. Turns out NodeList.prototype.isPrototypeOf(nodes) is by far the fastest. But in a normal use-case nodes instanceof NodeList would be fine too.

I personally would just not pick the isNodeList function, because its slow, custom and too much overhead.