CODEWITHSUNDEEP
javascript
simon xu
simon xu

Reputation: 982

How to detect HTMLCollection/NodeList in JavaScript?

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?

Upvotes: 36

Views: 35031

Answers (8)

risingPhoenix1979
risingPhoenix1979

Reputation: 1154

Below is a JavaScript function to check if an HTMLCollection or NodeList exists in the DOM of a web page, and the code below was tested in the Chrome Dev Tools > Console tab of https://stackexchange.com/:

function ifElemExists(elem) {
    if((elem instanceof NodeList) || (elem instanceof HTMLCollection)) return true;

    return false;
}

const elem1 = document.querySelector('.blah');
const elem2 = document.querySelectorAll('.siteHeader');
const elem3 = document.getElementById('footer');
const elem4 = document.getElementsByClassName('blah');

console.log(ifElemExists(elem1)); // Output: false
console.log(ifElemExists(elem2)); // Output: true
console.log(ifElemExists(elem3)); // Output: false
console.log(ifElemExists(elem4)); // Output: true

Upvotes: 0

vineethbc
vineethbc

Reputation: 900

The following should return true, if nodes is of type NodeList

NodeList.prototype.isPrototypeOf(nodes)

@DavidSpector, for HTMLCollection you can similarly use :

HTMLCollection.prototype.isPrototypeOf(collection)

Upvotes: 53

eisbehr
eisbehr

Reputation: 12452

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.

Upvotes: 1

koech
koech

Reputation: 606

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);

Upvotes: 12

rosell.dk
rosell.dk

Reputation: 2502

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

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

Upvotes: 17

Tomalak
Tomalak

Reputation: 338326

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 (i.e. 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

Upvotes: 25

Guja1501
Guja1501

Reputation: 1028

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
  */
}

Upvotes: 13

Mohamed Moustafa
Mohamed Moustafa

Reputation: 289

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

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

Upvotes: 6

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