Front-End & Back-End Integration

I have a working front end written in plain HTML and JavaScript and a lightweight back end that also runs in JavaScript. Right now they operate in isolation. I need the two layers wired together so every piece of data the browser sends is correctly received, checked, and acted on by the server... (Budget: $30 - $250 USD, Jobs: API Integration, Backend Development, Frontend Development, HTML, Java, JavaScript, jQuery / Prototype, PHP)