Create node list from a single node in JavaScript

Question 1

Reviving this because I recently remembered something about JavaScript. This depends on how the NodeList is being checked, but..

const singleNode = ((nodeList) => (node) => {
  const layer = { // define our specific case
    0: { value: node, enumerable: true },
    length: { value: 1 },
    item: {
      value(i) {
        return this[+i || 0];
      }, 
      enumerable: true,
    },
  };
  return Object.create(nodeList, layer); // put our case on top of true NodeList
})(document.createDocumentFragment().childNodes); // scope a true NodeList

Now, if you do

const list = singleNode(document.body); // for example

list instanceof NodeList; // true
list.constructor === NodeList; // true

and list has properties length 1 and 0 as your node, as well as anything inherited from NodeList.

If you can't use Object.create, you could do the same except as a constructor with prototype nodelist and set this['0'] = node;, this['length'] = 1; and create with new.

ES5 version

var singleNode = (function () {
    // make an empty node list to inherit from
    var nodelist = document.createDocumentFragment().childNodes;
    // return a function to create object formed as desired
    return function (node) {
        return Object.create(nodelist, {
            '0': {value: node, enumerable: true},
            'length': {value: 1},
            'item': {
                "value": function (i) {
                    return this[+i || 0];
                }, 
                enumerable: true
            }
        }); // return an object pretending to be a NodeList
    };
}());

Question 2

Take any element already referenced in JavaScript, give it an attribute we can find using a selector, find it as a list, remove the attribute, return the list.

function toNodeList(elm){
    var list;
    elm.setAttribute('wrapNodeList','');
    list = document.querySelectorAll('[wrapNodeList]');
    elm.removeAttribute('wrapNodeList');
    return list;
}

Extended from bfavaretto's answer.

function toNodeList(elm, context){
    var list, df;
    context = context // context provided
           || elm.parentNode; // element's parent
    if(!context && elm.ownerDocument){ // is part of a document
        if(elm === elm.ownerDocument.documentElement || elm.ownerDocument.constructor.name === 'DocumentFragment'){ // is <html> or in a fragment
            context = elm.ownerDocument;
        }
    }
    if(!context){ // still no context? do David Thomas' method
        df = document.createDocumentFragment();
        df.appendChild(elm);
        list = df.childNodes;
        // df.removeChild(elm); // NodeList is live, removeChild empties it
        return list;
    }
    // selector method
    elm.setAttribute('wrapNodeList','');
    list = context.querySelectorAll('[wrapNodeList]');
    elm.removeAttribute('wrapNodeList');
    return list;
}

There is another way to do this I thought of recently

var _NodeList = (function () {
    var fragment = document.createDocumentFragment();
    fragment.appendChild(document.createComment('node shadows me'));
    function NodeList (node) {
        this[0] = node;
    };
    NodeList.prototype = (function (proto) {
        function F() {} // Object.create shim
        F.prototype = proto;
        return new F();
    }(fragment.childNodes));
    NodeList.prototype.item = function item(i) {
        return this[+i || 0];
    };
    return NodeList;
}());

Now

var list = new _NodeList(document.body); // note **new**
list.constructor === NodeList; // all these are true
list instanceof NodeList;
list.length === 1;
list[0] === document.body;
list.item(0) === document.body;

Question 3

If you're targeting browsers that support document.querySelectorAll, it will always return a NodeList. So:

var nodelist = document.querySelectorAll("#mydiv");

Question 4

Yet another way to do this based on Reflect.construct: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Reflect/construct

As in other cases it requires patching NodeList.prototype.item to make calls to this function work.

NodeList.prototype.item = function item(i) {
    return this[+i || 0];
};
let nl = Reflect.construct(Array, [], NodeList);

To create it with nodes pass array of nodes as second argument. This method passes checks:

list instanceof NodeList; // true
list.constructor === NodeList; // true

Array, created with it, is iterable with for..of, forEach and other standard methods and you can add elements into it with simple nl[n] = node;.

Question 5

var nodeList = document.createDocumentFragment();
nodeList.appendChild(document.getElementById("myDiv"));