Async Array Iterator

iterate.js

Array.prototype.iterate = function (cb, done, timeout) {
  ((timeout != undefined) || (typeof timeout == "object") || (timeout = 5000));

  var total = this.length;
  var result = [];

  if (total == 0) {
    return done(null, result);
  }

  var sent = false;
  this.forEach(function (e, i) {
    setTimeout(function () {
      cb(e, function (data) {
        if (data instanceof Error) {
          if (!sent) {
            done(data, null);
            sent = true;
          }
        } else {
          result[i] = data;

          if (--total == 0 && !sent) {
            done(null, result);
            sent = true;
          }
        }
      })
    });
  });

  if (timeout != null) {
    setTimeout(function () {
      if (total != 0 && !sent) {
        done(Error("timeout"), null);
        sent = true;
      }
    }, timeout);
  }
};

example

[1, 2, 3, 4].iterate(function(obj, done) {
  console.log(obj, obj * 2);
  done(obj * 2);
}, function(err, result) {
  if(err) {
    return console.error(err);
  }
  console.log(result);
});

1 2
2 4
3 6
4 8
[2, 4, 6, 8]

another example

[1, 2, 3, 4].iterate(function(obj, done) {
  setTimeout(function() {
    console.log(obj + " finished");
    done(obj * 1000);
  }, 1000 * obj);
}, function(err, result) {
  if(err) {
    return console.error(err);
  }
  console.log(result);
});

1 finished
2 finished
3 finished
4 finished
[1000, 2000, 3000, 4000]

result doesn't change result index if data came with different order

[1, 2, 3, 4].iterate(function(obj, done) {
  setTimeout(function() {
    console.log(obj + " finished");
    done(obj * 1000);
  }, 4000 - 1000 * obj);
}, function(err, result) {
  if(err) {
    return console.error(err);
  }
  console.log(result);
});

4 finished
3 finished
2 finished
1 finished
[1000, 2000, 3000, 4000]

timeout example

[1, 2, 3].iterate(function() { /* missing done or it isn't finished over the time */}, function(err, results) { 
  console.log(err, results); // err says its timeout
});

[1].iterate(function(i, done) {
  setTimeout(function() {
    done(i);
  }, 10000);
}, function(err, results) {
  if(err) // again err is true because it timeout default is 5000 (5sec) and done is calling after 10second..
});

// to prevent this you can use third parameter
[1].iterate(function(i, done) {
  setTimeout(function() {
    done(i);
  }, 10000);
}, function(err, results) {
 // no problem
}, 15000);

// for disable timeout use null 
[1].iterate(function(i, done) {
  setTimeout(function() {
    done(i);
  }, 10000);
}, function(err, results) {
 // no problem
}, null);

error example

[1, 2, 3].iterate(function(i, done) {
  if(i == 2) {
    done(Error("something bad happened!"));
  } else {
    done(i);
  }
}, function(err, results) {
  console.log(err, results); // err = something bad.., results = empty
})