Out of the box, express-flash only supports strings, occasionally it's useful to have some json stick around after redirects. This middleware tacks on a jsonFlash function to accomplish that. If you require this middleware you have both flash() and jsonFlash();

Express JsonFlash

var flash = require('express-flash')();

module.exports = function() {
	return function(req, res, next) {
		flash(req, res, function() {
			req.jsonFlash = function() {
				if (arguments.length === 1) {
					var data = req.flash(arguments[0]);
					if (data.length) {
						return JSON.parse(data);
					}
				} else {
					var key = arguments[0];
					var value = JSON.stringify(arguments[1]);
					req.flash(key, value);
				}
			};
		});
		next();
	};
};