Poor man's yepnope

myloader.js

function MinimalPromise() {
  this.callbacks = [];

  this.then = function(cb) {
    this.callbacks.push(cb);
    if (this.result !== undefined && !(this.result instanceof MinimalPromise)) {
      this._pump();
    }
    return this;
  }.bind(this);
  
  this.resolve = function(result) {
    this.result = result;
    this._pump();
  }.bind(this);

  this._pump = function() {
    while (this.callbacks.length) {
      var cb = this.callbacks.shift();
      this.result = cb(this.result);
      if (this.result instanceof MinimalPromise) {
        this.result.then(function(result) {
          this.result = result;
          this._pump();
        }.bind(this))
        break
      }
    }
  }.bind(this);
  
  return this;
}
function loadSource(srcs, idx) {
  idx = idx || 0;
  var d = new MinimalPromise();
  var script_elem = document.createElement('script');
  
  script_elem.addEventListener('error', function(ev) {
    loadSource(srcs, idx+1).then(d.resolve);
  }, false);
  
  script_elem.addEventListener('load', function(ev) {
    d.resolve(srcs[idx]);
  }, false);
  
  script_elem.setAttribute('src', srcs[idx]);
  document.body.appendChild(script_elem);
  return d;
}
function all(promises) {
  var results = [];
  var resolved = 0;
  var expected = promises.length;
  var d = new MinimalPromise();
  for (var i = 0; i < expected; i++) {
    var p = promises[i];
    p.then(function(result) {
      results[i] = result;
      resolved += 1;
      if (resolved === expected) {
        d.resolve(results);
      }
    });
  }
  return d;
}
//
// Run a list of functions in parallel, returning
// a promise that will fire when they're all done.
//
function parallel(funcs) {
  var dlist = [];
  for (var i = 0; i < funcs.length; i++) {
    dlist.push(funcs[i]());
  }
  return all(dlist)
  return d;
}
//
// Run a list of functions one after another,
// returning a promise that will
// fire when they're all done.
//
function sequentially(funcs) {
  var d = new MinimalPromise();
  for (var i = 0; i < funcs.length; i++) {
    d.then(function(funcs, i) {
      return funcs[i]();
    }.bind(this, funcs, i));
  }
  d.resolve(true);
  return d;
}

function l_parallel(funcs) {
  return function() {
    return parallel(funcs);
  }
}
function l_sequentially(funcs) {
  return function() {
    return sequentially(funcs);
  }
}
function l_loadSource(libs) {
  return function() {
    return loadSource(libs);
  }
}