Convert xlsx file and formula into a JS API

We currently use an excel spreadsheet to make some function and calculate everything thru formula and multiple sheet. We would like to port it on the web in order to ease the process. We just need to transform the formula part in a sort of JS API, that will be called by the website. So basically we want you to create a JS file with namespace and separate function. Private function should do the logic and public function should be called to get result. We could provide basic prototype and excel spreadsheet in order for you to get a clear picture of the project. This is a one time schedule thing.