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wire up express routes to promise-returning functions


Unstable: Expect patches and features, possible api changes.


$ npm install qed


Say you're in the context of an express (or express-like) app, and you've got some end points that look like this:

app.get('/fruits/veggies/:quantity', function (req, res) {
  // do stuff

Well, now try mixing this in where "do stuff" is a function which returns a Promise:

app.get('/fruits/veggies/:quantity', function (req, res) {
  doStuff(req.params.quantity).then(function (val) {
  }, function(err) {
    res.send(500, err)

Well, with qed we can make this absurdly simple example a bit nicer with some opinionated defaults:

var qed = require('qed')

  qed(doStuff, 'req.params.quantity'))

The less blood there is at the interface layer, the more you can focus on your application. qed handles mapping between your application-level functions and all the gooky HTTP stuff, so you can keep your implementation framework agnostic.

But, you say, you want to be more hands-on with the http response - maybe a special case status code?'/fruits/order',
  qed(makeOrder, 'req.user', 'req.body')
    .response(202)) // HTTP 202 - Accepted

Or even more holy-cow-hands-on HTTP madness:'/fruits/order',
  qed(makeOrder, 'req.user', 'req.body')
    .response(function(err, result) {
      if (err) { return this.send(500, err.message)}
      this.send(202, result)

And, if you want to handle your req-res stuff manually you may do so:

// make sure your function has parameters of exactly `req, res`
function boxes(req, res) {


// pass it to qed without specifying any accessors

Note, if you don't return a promise, then you're totally responsible for sending your own response.

The power is yours.


qed(promiser, params...)

promiser is a promise-returning function. params is 0 or more accessor strings corresponding (in order) to promiser's parameters.

For example, if you had a promiser like:

getBooksByAuthor(authorName, limit) {
  limit = limit || 25
  return promiseOfDbQuery()

and you were hooking it up to a url like /author/:author/books?limit=:limit, you might have:

qed(getBooksByAuthor, '', 'req.query.limit')

Accessor strings used to map params must start with req or res, but can access any property thereof. Go nuts with your middleware.

qed returns a function with the (req, res) signature that express is expecting in a route handler. When invoked, this function will map any params from the Request and Repsonse objects and call promiser with these arguments. If the promise is rejected, it will respond with an error. (See Errors) When the promise is resolved, it will send the response, by default as a 200.


Chain after a qed call to override the default response code when the promise is resolved to use statusCode instead of 200.

qed#response(handlerFunction) where handlerFunction(err, result) {}

Chain after a qed call to intercept the response. handlerFunction is invoked with arguments err (the reason if the promise is rejected) and result (the value if the promise is fulfilled). this is the Response object. No return value is expected.

qed.on(event, listner)

Attach an event listener. Also suports standard node EventEmitter methods. qed emits an error event (see below).


By default, if the promise is rejected, qed will respond with a 500 error and will send the Error#message property to the response. If the error thrown has a statusCode property in the 400 or 500 range, qed will use that for the response. Strongly consider using the qed#response handler to encapsulate your http-specific logic.

qed is also an event emitter, and it will emit an error event. (Note: normally node EventEmitters will throw any error events if there are no listeners. However, in this case, qed does not emit the error event if there are no listeners, so there shouldn't be any surprises)

Running the tests

From the package root directory

$ npm install
$ npm test


jden <>


MIT, (c) 2013 jden See

quod erat demonstrandum.