Creating truly asynchronous functions

gistfile1.js

/*
When coding in Node.js, you will often/most likely be dealing with some I/O, which involves asynchronous processes. Therefore, building a standard for coding is paramount. 

Consider the following code:
*/

var fs = require('fs');

function logA(command, data, done) {
  if(command === 'write') {
    fs.writeFile('somefile', data, function(err) {
      console.log(data);
      done();
    });
  } else {
    console.log(data);
    done();
  }
}

/**
 * now consider the following use case:
 */

logA('read', 'hello', function(err) {
  console.log('world');
});

console.log('welcome');

/**
 * The output will be:
 * > hello
 * > world
 * > welcome
 */
 
// Now consider the following use case?
logB('write', 'hello', function(err) {
  console.log('world');
});

console.log('Welcome');

/**
 * The output would be:
 * > welcome
 * > hello
 * > world
 */

/**
 * What happened? Crap, this `logA` function is _sometimes_ synchronous and _sometimes_ asynchronous!
 * It gets people confused. To solve this, you always make it async.
 */
 
function modifiedLogA(cmd, data, done) {
  if(cmd === 'write') {
    fs.writeFile('somefile', data, function(err) {
      console.log(data);
      done();
    });
  } else {
    // This gets put into the event-loop, for the _next_ iteration
    // now this function is truly async regardless of conditions.
    setImmediate(function() {
      console.log(data);
      done();
    });
  }
}