methods.js

// Assume errorPage, jsonBody, formBody exist within scope.

function methods(routes, handleHttpForms) {
    if (handleHttpForms)  {
        return createHttpFormsRequestHandler(routes)
    }
    return requestHandler

    function requestHandler(req, res) {
        var method = req.method,
            f = routes[method]

        if (f) {
            return f.apply(this, arguments)
        }
        errorPage(req, res, 405)
    }
}

function createHttpFormsRequestHandler(routes) {
    return httpFormsRequestHandler

    function httpFormsRequestHandler(req, res) {
        if (req.method !== "POST") {
            return requestHandler.apply(this, arguments)
        }

        var args = arguments,
            self = this

        contentTypes(req, {
            "application/json": jsonBody,
            "default": formBody
        })(req, res, extractMethod)

        function extractMethod(body) {
            var method = body._method,
                f = routes[method]

            if (f) {
                return f.apply(self, args)
            }
            errorPage(req, res, 405)
        }
    }
}