How to get the index of the element in javascript?

Question

The NodeList don't have a indexOf(element) method? So, how can I get the element index?

Answer 1

You can use Array.prototype.indexOf.call() like this

let nodes = document.getElementsByTagName('*');
Array.prototype.indexOf.call(nodes, document.body);

Answer 2

The NodeList objet is an Array-like object. So it's possible to "convert" it into an Array using Array.prototype.slice.call()

var arr = Array.prototype.slice.call(yourNodeListObject); // Now it's an Array.
arr.indexOf(element); // The index of your element :)

On browsers that support ES6 you can also do this with Array.from()

const arr = Array.from(yourNodeListObject);

or using the spread operator ...

const arr = [...yourNodeListObject];

Answer 3

By iterating over the elements, and checking if it matches.

Generic code that finds the index of the element within it's parents childNodes collection.

function index(el) {
    var children = el.parentNode.childNodes,
        i = 0;
    for (; i < children.length; i++) {
        if (children[i] == el) {
            return i;
        }
    }
    return -1;
}

Usage:

// should return 4
var idx = index(document.body.childNodes[4]);

EDIT: I can't delete an accepted answer, but @kennebec's answer below is much better, which I'll quote verbatim:

You can use Array.prototype.indexOf.call() like this

let nodes = document.getElementsByTagName('*');
Array.prototype.indexOf.call(nodes, document.body);

Answer 4

Let us say you have the following line:

const list=document.querySelectAll('.some_class .someother_class');

list will be a nodelist. So we can convert the nodelist to an array and create a new array of indexes as follows:

const indexArr= [...list].map( element => return [...list].indexOf(element) );

indexArr contains all the indexes of elements in the original list.

Answer 5

Just add one line in your script:

NodeList.prototype.indexOf = Array.prototype.indexOf;   // for IE11

Then use indexOf as usual:

var index = NodeList.indexOf(NodeElement);