Waits for functions to complete before running complete

README.md

Unfinished and not tested beyond my own case.

Usage

var wait = new Wait();
wait.complete(function () {
  console.log('we are done - now report');
});

$.get(url, wait.until(function (data) {
  // do something with data
});

db.users.find(wait.until(function (err, docs) {
  // we've found users in the mongo db
}));

wait.js

Wait = function (complete) {
  if (complete) this.oncomplete = complete;
};

Wait.prototype = {
  debug: false,
  log: function () {
    if (!this.debug) return;
    var args = [].slice.apply(arguments);
    if (typeof args[0] == 'string') args[0] = '[wait] ' + args[0];
    else args.unshift('[wait]');
    console.log.apply(console, args);
  },
  oncomplete: function () {},
  complete: function (fn) {
    if (fn === undefined) {
      this.oncomplete();
    } else {
      this.oncomplete = fn;      
    }
  },
  tasks: 0,
  done: function () {
    this.tasks--;
    this.log('tasks left: ' + this.tasks);
    if (this.tasks == 0) {
      this.log('triggering complete')
      this.complete();
    }
  },
  until: function (task, context) {
    var self = this,
        name = (arguments.callee.name || 'anonymous');
    this.tasks++;

    context || (context = this);
    this.log('new task: %s, total: %d', (arguments.callee.name || 'anonymous'), this.tasks);
    return function () {
      self.log('running %s', name);
      var ret,
          args = [].slice.apply(arguments);
      // args.push(self.done);
      try {
        ret = task.apply(context, args);
      } catch (e) {
        console.error(e);
      }
      self.done();
      return ret;      
    };
  },
  run: function (task, context) {
    return this.add(task, context)();
  }
};

if (typeof module !== undefined && module.exports !== undefined) {
  module.exports = Wait;
}

Maybe have a look at when.js's when.all and when.reduce. They can join multiple tasks, and might do what you need. Here's a quick take on the original wait usage with when.js:

var when, apply, p1, p2;

when = require('when');
apply = require('when/apply');

var p1, p2;

p1 = $.get(url);

p2 = when.defer();
db.users.find(function (err, docs) {
  // we've found users in the mongo db
  p2.resolve(docs);
});

when.all([p1, p2],
    function(results) {
        // results[0] is p1 result
        // results[1] is p2 result
        console.log('we are done - now report');
    }
);

// Or use when/apply to spread results onto function args
when.all([p1, p2],
    apply(function(data, docs) {
        console.log('we are done - now report');
    })
);

// Could also use when.reduce (promise-aware Array.proto.reduce)
// to reduce the results.
// Here's a simple string concat
when.reduce([p1, p2],
    function(finalResult, current) {
        return finalResult + current;
    }, '') // initial value is empty string
.then(
    function(finalResult) {
        console.log('we are done - now report');    
    }
);

Unlike jQuery's Deferred, when.js is compliant with the defacto standard (CommonJS Promises/A), runs in browsers and node (and probably RingoJS), and even converts non-compliant promises like $.Deferred to compliant ones. #WIN

FWIW, yep, when.js 1.0.2 (probably earlier versions, too) works in Ringo 0.8.