Easy Deferrables For JavaScript

defers.js

/* See also: http://cl.ly/0Q1n1P0R223E1224332M/o */

/* the main trick */
function deferrable(f) {
  return function() {
    return (function(f, args) {
      return function() {
        return f.apply(null, args);
      };
    })(f, arguments);
  }
}

/* the function we want to be deferred */
function read_file(name) {
  console.log('reading ' + name);
  return name !== 'foo.js'; // success when name's not `foo.js`
}

/* some function that executes a list of another 
   function in a smart way

   prepares them, breaks them, anything... */
function smart_exec() {
  var fs = arguments, // array of functions
      flen = fs.length;
  for (var i = 0; i < flen; i++) {
    if (!fs[i]()) return; // if function not succeeded, stop the process
  };
}

/* we may emulate smart "break queue if failed" using && operator 
               or smart "break on first success" using || operator,
   but that'all.
 
   notice that `read_file('c')` is not executed here. */
read_file('a') && read_file('b') && read_file('foo.js') && read_file('c');
// > reading a
// > reading b
// > reading foo.js
// < false

/* we may use smart_exec in a way like this, but it looks like a crap

   yes, we may pass a list of files to some function and read them inside,
   but then we may call it not `smart_exec`, but rather `smart_read_file` */
smart_exec(function() { return read_file('a') }, function() { return read_file('b') },
           function() { return read_file('foo.js') }, function() { return read_file('c') });
// > reading a
// > reading b
// > reading foo.js
// < undefined

/* and so we transform `read_file` into deferrable... */
read_file = deferrable(read_file);

/* ... cool enough, isn't it?

   notice that `read_file('c')` is not executed here... */
smart_exec(read_file('a'), read_file('b'), read_file('foo.js'), read_file('c'));
// > reading a
// > reading b
// > reading foo.js
// < undefined