nonblocking_loop.js

// An example of how to work with an array in a non-blocking
// loop.

// This will store our results.
var result = {
  count: 0,
  sum: 0,
  toString: function () {
    return "Count: " + result.count + ", Sum: " + result.sum;
  }
};

// Let's actually declare our addtion function here.
function add(array, done) {

  // We're using setImmediate to give control back to the Node process.
  // We will run once, then queue up the next callback.
  function addValue (value, callback) {
    return setImmediate(function () {
      result.count += 1;
      result.sum += value;
      callback();
    });
  };

  // I don't think there's anything here that could throw an error,
  // but we don't actually want to throw the error regardless.
  // Instead, lets catch it and include it in the callback.
  try {
    if (array.length > 0) {
      addValue(array.shift(), function () {
        add(array, done);
      });
    } else {
      // There are no more items in the array, so fire the callback.
      done(null, result);
    }
  } catch (e) {
    done(e, result);
  }

};

// Declare our array and run our code.
var array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
add(array, function(err, res) {
  if (err) {
    console.error("Error: " + err);
    return;
  }
  console.log("Result: " + res);
});