JSFiddle - React, Tailwind, and code Playground
by mhouser_nowmediagroup
HTML
<div id="output"></div>
<form accept-charset="UTF-8" action="https://blah.formy.net" class="infusion-form" id="inf_form_2bddccc1e5f020a10eb95af4f96f99ca" method="POST">
<input name="inf_form_xid" type="hidden" value="2bddccc1e5f020a10eb95af4f96f99ca">
<input name="inf_form_name" type="hidden" value="Hidden Form&#a;(E = Hidden)">
<input name="inf_field_Email" type="email" value="null" style="">
<button type="submit">Sign Up</button>
<input type="hidden" id="timeZone" name="timeZone" value="America/Los_Angeles"></form>
JavaScript
jQuery(window).on("load", function(){
var link = window.location.href + "&stuff&things&email=radfish%40skewlofroot.com&other_stuff_too"
var start_index, end_index
var current_index = (/%40/.exec(link)).index
while(link[current_index] != '=')
start_index = current_index--
while(link[current_index] != '&')
end_index = ++current_index
var email_address = (link.substring(start_index, end_index)).replace("%40", '@')
jQuery("#inf_form_2bddccc1e5f020a10eb95af4f96f99ca > [name^='inf_field_Email']").val(email_address)
})