JavaScript to trigger an API Call

Hi, We are looking for a Senior JavaScript developer to write a script to be used on website's header to: - Track if the website user is coming from a Google Ad Campaign - If yes, then pass on the below information to an API call: --- IP Address of the user, Serial number for the website (pre-defined in JS), Google analytics session code (if GA is installed already), User's device info (OS, Browser, Screen) We are open for discussion, but the selected developer can decide if the code is to all inclusive in the header (if it has a small footprint) Or code can call another script when conditions are matched to send information to the API. We need the code to be very optimised, have a small(est) footprint and size, and just works every time :) Ideally JS code is to be written in core JS so to keep away any possible bloat. Generic bids will be ignored. Please do convince with your skillset/ ideas for us to shortlist you. Thanks.