Is it possible to have the same config file for server node.js and client js code?
Now I use .json config for node.js, but can convert it to any format
Without more information, all I can offer is a simple suggestion: Require.js. You can reference a config module in the Node.js code and reference it in the client script. Just make sure that the config file can be served to the client.
// Example reference
var config = require('./data/config.js');