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copied!<p>This should do it:</p> <pre><code>function getNext(num) { var alphabet = "123456789ABCDEFGHJKLMNPQRSTUVWXYZ"; var digits = num.toUpperCase().split(""), len = digits.length, increase = true; if (len != 3) throw new Error("Invalid serial number length in getNext: "+num); for (var i=len-1; increase && i>=0; i--) { var val = alphabet.indexOf(digits[i]); if (val == -1) throw new Error("Invalid serial number digit in getNext: "+num); val++; if (val < alphabet.length) { digits[i] = alphabet[val]; increase = false; } else { // overflow digits[i] = alphabet[0]; } } if (increase) // is still true throw new Error("Serial number overflow in getNext"); num = digits.join(""); return num; } </code></pre> <p>Since you are working with a nearly alphanumeric alphabet, a <code>parseInt</code>/<code>toString</code> with radix 33 might have done it as well. Only you need to "jump" over the <code>0</code>, <code>I</code> and <code>O</code>, that means replacing <code>0,A,B…</code> by <code>A,B,C…</code>, replacing <code>H,I,J…</code> by <code>J,K,L…</code> and replacing <code>M,N,O…</code> by <code>P,Q,R…</code> (and everything back on deserialisation) - which might be OK if JS has a numeric <code>char</code> datatype, but I think it's easier to do it manually as above.</p> <p>If you're curious:</p> <pre><code>String.prototype.padLeft = function(n, x) { return (new Array(n).join(x || "0")+this).slice(-n); }; function getNext(num) { var alphabet = "123456789ABCDEFGHJKLMNPQRSTUVWXYZ"; var back = {}, forth = {}; for (var i=0; i<alphabet.length; i++) { var a = alphabet[i], b = i.toString(36); back[a] = b; forth[b] = a; } return (parseInt(num.replace(/./g, function(c) { return back[c]; // base33 from alphabet }), alphabet.length) + 1) .toString(alphabet.length) .padLeft(3) .replace(/./g, function(c) { return forth[c]; // base33 to alphabet }); } </code></pre>

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