JSFiddle - React, Tailwind, and code Playground
HTML
<form name="formName">
<input name="m" value="foo">
<input name="p" value="bar">
<input name="0.prop" value="111">
<input name="1.prop" value="222">
</form>
JavaScript
var i = 0;
var s = i + '.prop';
var v = document.formName[s].value;
alert(v);