Spreadsheet program in under 30 lines of JavaScript

spreadsheet.js

//Written by: http://ondras.zarovi.cz/
//http://jsfiddle.net/ondras/hYfN3/

// <p>Inspired by <a href="http://thomasstreet.net/blog/spreadsheet.html">http://thomasstreet.net/blog/spreadsheet.html</a>. Features:</p>

// <ul>
//     <li>Under 30 lines of vanilla JavaScript</li>
//     <li>Libraries used: <strong>none</strong></li>
//     <li>Excel-like syntax (formulas start with "=")</li>
//     <li>Support for arbitrary expressions (=A1+B2*C3)</li>
//     <li>Circular reference prevention</li>
//     <li>Automatic localStorage persistence</li>
// </ul>

// <table></table>
    
// <footer><p>&copy; 2013 <a href="http://ondras.zarovi.cz/">Ondřej Žára</a></p></footer>

for (var i=0; i<6; i++) {
    var row = document.querySelector("table").insertRow(-1);
    for (var j=0; j<6; j++) {
        var letter = String.fromCharCode("A".charCodeAt(0)+j-1);
        row.insertCell(-1).innerHTML = i&&j ? "<input id='"+ letter+i +"'/>" : i||letter;
    }
}

var DATA={}, INPUTS=[].slice.call(document.querySelectorAll("input"));
INPUTS.forEach(function(elm) {
    elm.onfocus = function(e) {
        e.target.value = localStorage[e.target.id] || "";
    };
    elm.onblur = function(e) {
        localStorage[e.target.id] = e.target.value;
        computeAll();
    };
    var getter = function() {
        var value = localStorage[elm.id] || "";
        if (value.charAt(0) == "=") {
            with (DATA) return eval(value.substring(1));
        } else { return isNaN(parseFloat(value)) ? value : parseFloat(value); }
    };
    Object.defineProperty(DATA, elm.id, {get:getter});
    Object.defineProperty(DATA, elm.id.toLowerCase(), {get:getter});
});
(window.computeAll = function() {
    INPUTS.forEach(function(elm) { try { elm.value = DATA[elm.id]; } catch(e) {} });
})();