js 生成 UUID

function(len, radix) {
    var chars = ‘0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz‘.split(‘‘);
    var uuid = [],
    radix = radix || chars.length;
    if (len) {
        for (var i = 0; i < len; i++) uuid[i] = chars[0 | Math.random() * radix];
    } else {
        var r;
        uuid[8] = uuid[13] = uuid[18] = uuid[23] = ‘-‘;
        uuid[14] = ‘4‘;
        for (var i = 0; i < 36; i++) {
            if (!uuid[i]) {
                r = 0 | Math.random() * 16;
                uuid[i] = chars[(i == 19) ? (r & 0x3) | 0x8 : r];
            }
        }
    }

    return uuid.join(‘‘);
}