Javascript - Singapore NRIC Checker

NIRCchecker.js

    function check_nric(nric_number) {
 
        var nric_first = '';
        var nric_last = '';
 
        var nric_code = -1;
        var nric_checksum = -1;
        var mod_calculate = -1;
 
        var checksum_boolean = false;
        var process_abort = false;
 
        var ST_hash = new Array();
        var FG_hash = new Array();
        var offset = 0;
 
        ST_hash["J"] = 0;
        ST_hash["Z"] = 1;
        ST_hash["I"] = 2;
        ST_hash["H"] = 3;
        ST_hash["G"] = 4;
        ST_hash["F"] = 5;
        ST_hash["E"] = 6;
        ST_hash["D"] = 7;
        ST_hash["C"] = 8;
        ST_hash["B"] = 9;
        ST_hash["A"] = 10;
 
        FG_hash["X"] = 0;
        FG_hash["W"] = 1;
        FG_hash["U"] = 2;
        FG_hash["T"] = 3;
        FG_hash["R"] = 4;
        FG_hash["Q"] = 5;
        FG_hash["P"] = 6;
        FG_hash["N"] = 7;
        FG_hash["M"] = 8;
        FG_hash["L"] = 9;
        FG_hash["K"] = 10;
 
        nric_number = nric_number.toString();
 
        if (nric_number.length != 9) {
            process_abort = true;
            checksum_boolean = false;
        }
 
        if (!process_abort) {
            nric_first = nric_number.substr(0, 1);
            nric_last = nric_number.substr(8, 1);
 
            switch (nric_first.toUpperCase()) {
                case "S":
                    nric_checksum = ST_hash[nric_last];
                    break;
                case "T":
                    nric_checksum = ST_hash[nric_last];
                    offset = 4;
                    break;
                case "F":
                    nric_checksum = FG_hash[nric_last];
                    break;
                case "G":
                    nric_checksum = FG_hash[nric_last];
                    offset = 4;
                    break;
                default:
                    checksum_boolean = false;
                    process_abort = true;
                    break;
            }
        }
 
        if (!process_abort) {
            mod_calculate = nric_number.substr(1, 1) * 2 +
                nric_number.substr(2, 1) * 7 +
                nric_number.substr(3, 1) * 6 +
                nric_number.substr(4, 1) * 5 +
                nric_number.substr(5, 1) * 4 +
                nric_number.substr(6, 1) * 3 +
                nric_number.substr(7, 1) * 2;
 
            nric_code = (mod_calculate + offset) % 11;
 
            if (nric_code == nric_checksum) {
                checksum_boolean = true;
            }
        }
        return checksum_boolean;
    }