Sheet

An Excel-like spreadsheet with arbitrary expressions and persistence using localStorage golfed under 256 bytes with aem1k, subzey, xem, rlauck, odensc, mmastrac, and corruptio

This one was fun. It started with a tutorial about making a Speadsheet in AngularJS in 20 minutes, then 30 lines of JS and ultimately aem1k optimized the whole thing down to 468 bytes, and the fun began.

Then came the league of size optimizer extaordinaires, aem1k, subzey, xem and rlauck, and together we golfed this puppy down to 256 bytes.

Source code

 <script>(o=b=>{for(j in a="ABCD")for(i in a)y=a[i]+-~j,b?document.write([["<p>"][i]]+y+"<input onfocus=value=[l[id]] onblur=l[id]=value;o() id="+y+" value="+[l[y]]+"> "):eval(y+(".value"+l[y]).replace(/[A-Z]\d/g," +$&.value"))})(o(l=localStorage))</script>

Yup. 256 bytes. See the commit history