array-index elements.

index.js

'use strict'

var h1 = function (tag, props, children) {
	return {tag: tag, props: props, children: children}
}

var h2 = function (tag, props, children) {
	return {tag: tag, props: props, children: children, 9: ''}
}

var start, end;
var iter = 500000;
var nodes1 = []
var nodes2 = []

{
	start = Date.now()

	for (var i = 0; i < iter; ++i) {
		var node = h1('h'+i, {i}, ['index: ', i]);
		node.tag = 'i:' + (i + 1)

		if (node.tag === undefined) {
			throw 'failed!'
		}

		nodes1.push(node);
	}

	console.log('0', Date.now() - start)
}

{
	start = Date.now()

	for (var i = 0; i < iter; ++i) {
		var node = h2('h'+i, {i}, ['index: ', i]);
		node[2] = 'i:' + (i + 1)

		if (node[2] === undefined) {
			throw 'failed!'
		}

		nodes2.push(node);
	}

	console.log('1', Date.now() - start)
}