async_experiments.js

// test_and_load does two things.  First it checks to see if a filepath
// is really a file and not a directory ot something crazy.
// If it's not a file it emits "undefined" (except for one case where null is used)
// If it is a file, then it emits the file's contents
// Any errors in fs.stat or fs.fileRead are passed through as is.

// In these examples, we're assuming that the fs module is of the same
// style as the function comsuming it.  So we're showing a small example of
// producer and consumer for each of the styles.

// simple continuable with seperate callback and errback
function test_and_load(filename) { return function (callback, errback) {
  fs.stat(filename)(function (stat) {

    // Filter out non-files
    if (!stat.isFile()) { callback(); return; }

    // Otherwise read the file in
    fs.readFile(filename)(callback, errback);

  }, errback);
}}

// simple continuable with single combined callback
function test_and_load(filename) { return function (callback) {
  fs.stat(filename)(function (stat) {

    // Pass along any errors before we do anything
    if (stat instanceof Error) { callback(stat); return; }

    // Filter out non-files
    if (!stat.isFile()) { callback(); return; }

    // Otherwise read the file in
    fs.readFile(filename)(callback);

  });
}}

// inimino style continuables
function test_and_load(filename) { return function (cont) {
  fs.stat(filename)(rightContinuation(cont)(function (stat) {

    // Filter out non-files
    if (!stat.isFile()) { cont(); return; }

    // Otherwise read the file in
    fs.readFile(filename)(cont);

  }));
}}


// http://github.com/bentomas/node-continuables
function test_and_load(filename) {
  return fs.stat(filename)(function (stat) {
    
    // Pass along any errors before we do anything
    if(stat instanceof Error) { return; }
    
    // Filter out non-files
    if (!stat.isFile()) { return null; }

    // Otherwise read the file in
    return fs.readFile(filename);

  });
}

// promise based with node-promise helpers (github.com/kriszyp/node-promise)
var when = require("promise").when;
function test_and_load(filename) {
  return when(fs.stat(filename), function (stat) {
 
    // Filter out non-files
    if (!stat.isFile()) { return; }
 
    // Otherwise read the file in
    return fs.readFile(filename);
    
  });
}
 
 
// promise based with CommonJS monkey patch (github.com/kriszyp/node-commonjs/blob/master/patch-promise.js)
function test_and_load(filename) {
  return fs.stat(filename).then(function (stat) {
 
    // Filter out non-files
    if (!stat.isFile()) { return; }
 
    // Otherwise read the file in
    return fs.readFile(filename);
    
  });
}


// promise based (how it works in current node)
function test_and_load(filename) {
  var promise = new process.Promise();
  fs.stat(filename).addCallback(function (stat) {

    // Filter out non-files
    if (!stat.isFile()) { promise.emitSuccess(); return; }

    // Otherwise read the file in
    fs.readFile(filename).addCallback(function (data) {
      promise.emitSuccess(data);
    }).addErrback(function (error) {
      promise.emitError(error);
    });

  }).addErrback(function (error) {
    promise.emitError(error);
  });
  return promise;
}