src/base.js
function optionsObject(params, callback) {

    var headers = params.Headers;
    headers['Origin'] = params['Origin'];
    headers['Access-Control-Request-Method'] = params['AccessControlRequestMethod'];
    headers['Access-Control-Request-Headers'] = params['AccessControlRequestHeaders'];

    submitRequest.call(this, {
        Action: 'name/cos:OptionsObject',
        method: 'OPTIONS',
        Bucket: params.Bucket,
        Region: params.Region,
        Key: params.Key,
        headers: headers,
    }, function (err, data) {
        if (err) {
            if (err.statusCode && err.statusCode === 403) {
                return callback(null, {
                    OptionsForbidden: true,
                    statusCode: err.statusCode
                });
            }
            return callback(err);
        }

        var headers = data.headers || {};
        callback(null, {
            AccessControlAllowOrigin: headers['access-control-allow-origin'],
            AccessControlAllowMethods: headers['access-control-allow-methods'],
            AccessControlAllowHeaders: headers['access-control-allow-headers'],
            AccessControlExposeHeaders: headers['access-control-expose-headers'],
            AccessControlMaxAge: headers['access-control-max-age'],
            statusCode: data.statusCode,
            headers: data.headers,
        });
    });
}
function optionsObject(params, callback) {

    var headers = params.Headers;
    headers['Origin'] = params['Origin'];
    headers['Access-Control-Request-Method'] = params['AccessControlRequestMethod'];
    headers['Access-Control-Request-Headers'] = params['AccessControlRequestHeaders'];

    submitRequest.call(this, {
        Action: 'name/cos:OptionsObject',
        method: 'OPTIONS',
        Bucket: params.Bucket,
        Region: params.Region,
        Key: params.Key,
        headers: headers,
    }, function (err, data) {
        if (err) {
            if (err.statusCode && err.statusCode === 403) {
                return callback(null, {
                    OptionsForbidden: true,
                    statusCode: err.statusCode
                });
            }
            return callback(err);
        }

        var headers = data.headers || {};
        callback(null, {
            AccessControlAllowOrigin: headers['access-control-allow-origin'],
            AccessControlAllowMethods: headers['access-control-allow-methods'],
            AccessControlAllowHeaders: headers['access-control-allow-headers'],
            AccessControlExposeHeaders: headers['access-control-expose-headers'],
            AccessControlMaxAge: headers['access-control-max-age'],
            statusCode: data.statusCode,
            headers: data.headers,
        });
    });
}
Options Object请求实现跨域访问的预请求。即发出一个 OPTIONS 请求给服务器以确认是否可以进行跨域操作。
@param  {Object}  params             参数对象，必须
@param  {String}  params.Bucket  Bucket名称，必须
@param  {String}  params.Region  地域名称，必须
@param  {String}  params.Key     object名称，必须
@param  {Function}  callback         回调函数，必须
@return  {Object}  err               请求失败的错误，如果请求成功，则为空。https://cloud.tencent.com/document/product/436/7730
@return  {Object}  data              返回的数据