Javascript Spreadsheet engine / library for displaying fields

I am looking into some kind of Javascript engine for tables that would allow me to define complex calculations in a standard spreadsheet format (Excel, WKS or even some text format), and then let me read it from that formatted file (on the server) into Javascript spreadsheet engine and map it to specific form fields.

The reason is that the various web applications I have linked to have a lot of complex formula logic and code it all in pure Javascript is time consuming and error prone. It would be much more efficient to write the formulas in a spreadsheet and copy it through the engine later to the web form.

It needs to be Javascript, so immediate form changes are recalculated in place, without having to go back to the server.

Any suggestions?