[JavaScript] Encode or decode GeoHash

geohash.js

function geohash(lat, lon, len)
{
    if (len) {
        len = Number(len);
        if (len < 1 || len > 12) {
            return false;
        }
    } else {
        len = 12;
    }

    var base32Chars = [
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'b', 'c', 'd', 'e', 'f', 'g',
        'h', 'j', 'k', 'm', 'n', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'
    ];

    var latInterval  = [-90.0, 90.0];
    var lonInterval = [-180.0, 180.0];
    var bits = [16, 8, 4, 2, 1];
    var bit = 0;
    var isEven = true;

    // Encode
    if (lon && /^[\d\.]+$/.test(lat + '' + lon)) {
        var charIndex = 0;
        var geohash = '';

        while (geohash.length < len) {
            if (isEven) {
                var middle = (lonInterval[0] + lonInterval[1]) / 2;
                if (lon > middle) {
                    charIndex |= bits[bit];
                    lonInterval[0] = middle;
                } else {
                    lonInterval[1] = middle;
                }
            } else {
                var middle = (latInterval[0] + latInterval[1]) / 2;
                if (lat > middle) {
                    charIndex |= bits[bit];
                    latInterval[0] = middle;
                } else {
                    latInterval[1] = middle;
                }
            }

            if (bit < 4) {
                bit++;
            } else {
                geohash += base32Chars[charIndex];
                bit = 0;
                charIndex = 0;
            }

            isEven = isEven ? false : true;
        }

        return geohash;
    }

    // Decode
    else if('string' === typeof lat && lat.length <= 12) {
        var geohash = lat;
        var base32DecodeMap  = {};
        for (i = 0, l = base32Chars.length; i < l; i++) {
            base32DecodeMap[base32Chars[i]] = i;
        }

        for (i = 0, l = geohash.length; i < l; i++) {
            if (!base32DecodeMap[geohash[i]]) {
                // Invalid GeoHash
                return false;
            }

            var currentChar = base32DecodeMap[geohash[i]];
            for (j = 0, jl = bits.length; j < jl; j++) {
                var mask = bits[j];

                if (isEven) {
                    if ((currentChar & mask) !== 0) {
                        lonInterval[0] = (lonInterval[0] + lonInterval[1]) / 2;
                    } else {
                        lonInterval[1] = (lonInterval[0] + lonInterval[1]) / 2;
                    }
                } else {
                    if ((currentChar & mask) !== 0) {
                        latInterval[0] = (latInterval[0] + latInterval[1]) / 2;
                    } else {
                        latInterval[1] = (latInterval[0] + latInterval[1]) / 2;
                    }
                }

                isEven = isEven ? false : true;
            }
        }

        if (true === lon) {
            return {
                swlat: latInterval[0],
                swlon: lonInterval[0],
                nelat: latInterval[1],
                nelon: lonInterval[1],
            };
        } else {
            return {
                lat: (latInterval[0] + latInterval[1]) / 2,
                lon: (lonInterval[0] + lonInterval[1]) / 2
            };
        }
    }
}