javascript - Simple jQuery call to change input value continues returning TypeError $(...) is null -

my hair falling out while i'm trying figure out why jquery keeps throwing typeerror think valid call replace input value in html.

the line below being called in 1 of functions change of input values name "form_key."

$('input[name="form_key"]').val("itworks!");

(resides in http://vt2.net/js/warp/warp.js)

there multiple pages have hidden input name , pages have more once, , i'm trying change value on page.

the page below has 1 firebug keeps showing typeerror no matter how many ways try replace value. http://vt2.net/my-test-product.html

it's simple , stupid keep missing it! ideas?

you use

http://vt2.net/js/lib/jquery/noconflict.js 

where define

// avoid prototypejs conflicts, assign jquery $j instead of $ var $j = jquery.noconflict(); 

so operation jquery, need use $j instead $

and $ prototype.js

function $(element) {   if (arguments.length > 1) {     (var = 0, elements = [], length = arguments.length; < length; i++)       elements.push($(arguments[i]));     return elements;   }   if (object.isstring(element))     element = document.getelementbyid(element);   return element.extend(element); }