co-nth-arg

v0.1.0 release

If the thunk you yielded in a Co wrapped generator function call the callback with more than 2 arguments, it will be returned as an array by Co. For example, below is an example from co/examples/requests.js:

co(function *(){
  for (var i = 0; i < urls.length; i++) {
    var url = urls[i];
    var res = yield get(url);
    console.log('%s -> %s', url, res[0].statusCode);
  }
})()

res here is an array contain response object and body since request's callback will be called with 3 arguments: function (error, response, body).

It's annoying that every time you deal with that kind of thunk you write code like

var _res = yield get(url);
var res = _res[0];

or:

var res = (yield get(url))[0];

So I write this module. If you are sure that you always need only one of the arguments, you can use co-nth-arg to wrap your thunkified function:

var co = require('co');
var nth = require('co-nth-arg');
var request = require('request');

get = nth(1, thunkify(request)); // or nth.first(thunkify(request));
getBody = nth(2, thunkify(request)); // or nth.second(thunkify(request));

co(function *() {
  var res = yield get('http://google.com');
  console.log(res.statusCode);
  console.log(res.headers);
  console.log(res.body.length);

  var bingBody = yield getBody('http://bing.com');
  console.log(bingBody.length);
})();

v0.2.0 update

Now support zeroth argument to deal with functions like fs.exists. and add nth.thunkify(n, fn) method:

var fs = require('fs');
var exists = nth(0, thunkify(fs.exists)); // or nth.zeroth(thunkify(fs.exists)) or nth.thunkify(0, fs.exists);

If you don't specify the n, this method will delegate fn to original thunkify(), so you can use nth.thunkify to replace the original one.