Calculates correct NUS matriculation number with check digit, given matriculation number with missing / wrong check digit, NUSNET ID or NUS email address, with either U or A prefix.

matric.js

var calculateNUSMatricNumber = function (id) {
    var matches = id.toUpperCase().match(/^A\d{7}|U\d{6,7}/);
    if (matches) {
        var match = matches[0];
 
        // Discard 3rd digit from U-prefixed NUSNET ID
        if (match[0] === 'U' && match.length === 8) {
            match = match.slice(0, 3) + match.slice(4);
        }
 
        var weights = {
            U: [0, 1, 3, 1, 2, 7],
            A: [1, 1, 1, 1, 1, 1]
        }[match[0]];
 
        for (var i = 0, sum = 0, digits = match.slice(-6); i < 6; i++) {
            sum += weights[i] * digits[i];
        }
 
        return match + 'YXWURNMLJHEAB'[sum % 13];
    }
};