I explored this a bit (based off of the javascript-based http://sheetjs.com/sexql/) but the biggest difficulty is that people use CSVs and excel files in completely different ways for the same general task. In particular, different people set up budget workbooks in very different ways. There are also input problems and invalid files to deal with, so even if you manage to craft a meaningful integration you'd still have to figure out how to determine the structure and fix subtle non-uniformities
WebSQL is remarkably simple to use, works on the most popular browsers on mobile and desktop, and gives you the power of SQL. In contrast, IME indexed db felt like pulling teeth. The discussions seem to suggest that institutional intransigence by Mozilla pushed the internet back a step. (And yes, SQLite + Emscripten is significantly slower than websql on chrome and iOS Safari)
Substack (yes, that substack) discussed this recently:
> a slick web page - this is very often (but not always) a sign of a library that put all of its time into slick marketing but has overly-broad scope and is very likely to become abandoned
There is a good reason why no one has unseated excel: it's easy to build the really easy 80%, but the last 20% is incredibly difficult and time consuming.
Excel only supports numbers that fit in an IEEE754 double, just like JavaScript.
There is some fancy logic to format numbers, however (including some mess for date codes). http://oss.sheetjs.com/ssf/ is a pretty decent implementation in JavaScript.
It's somewhat confusing. The structure is MIT licenses but the individual implementations have different licenses (for example, many functions were copied from OpenOffice (which is under Apache2 license)
I'm actually working on this, although for various reasons I had to reimplement the formula parser (corner cases are a pain). Screenshot (in progress): http://i.imgur.com/snyBhYH.png
