JavaScript Sync/Async forEach

An optionally-asynchronous forEach with an interesting interface.

Getting Started

This code should work just fine in Node.js:

First, install the module with: npm install async-foreach

var forEach = require('async-foreach').forEach;
forEach(["a", "b", "c"], function(item, index, arr) {
  console.log("each", item, index, arr);
});
// logs:
// each a 0 ["a", "b", "c"]
// each b 1 ["a", "b", "c"]
// each c 2 ["a", "b", "c"]

Or in the browser:

<script src="dist/ba-foreach.min.js"></script>
<script>
forEach(["a", "b", "c"], function(item, index, arr) {
  console.log("each", item, index, arr);
});
// logs:
// each a 0 ["a", "b", "c"]
// each b 1 ["a", "b", "c"]
// each c 2 ["a", "b", "c"]
</script>

In the browser, you can attach the forEach method to any object.

<script>
this.exports = Bocoup.utils;
</script>
<script src="dist/ba-foreach.min.js"></script>
<script>
Bocoup.utils.forEach(["a", "b", "c"], function(item, index, arr) {
  console.log("each", item, index, arr);
});
// logs:
// each a 0 ["a", "b", "c"]
// each b 1 ["a", "b", "c"]
// each c 2 ["a", "b", "c"]
</script>

The General Idea (Why I thought this was worth sharing)

The idea is to allow the callback to decide at runtime whether the loop will be synchronous or asynchronous. By using this in a creative way (in situations where that value isn't already spoken for), an entire control API can be offered without over-complicating function signatures.

forEach(arr, function(item, index) {
  // Synchronous.
});

forEach(arr, function(item, index) {
  // Only when `this.async` is called does iteration becomes asynchronous. The
  // loop won't be continued until the `done` function is executed.
  var done = this.async();
  // Continue in one second.
  setTimeout(done, 1000);
});

forEach(arr, function(item, index) {
  // Break out of synchronous iteration early by returning false.
  return index !== 1;
});

forEach(arr, function(item, index) {
  // Break out of asynchronous iteration early...
  var done = this.async();
  // ...by passing false to the done function.
  setTimeout(function() {
    done(index !== 1);
  });
});

Examples

See the unit tests for more examples.

// Generic "done" callback.
function allDone(notAborted, arr) {
  console.log("done", notAborted, arr);
}

// Synchronous.
forEach(["a", "b", "c"], function(item, index, arr) {
  console.log("each", item, index, arr);
}, allDone);
// logs:
// each a 0 ["a", "b", "c"]
// each b 1 ["a", "b", "c"]
// each c 2 ["a", "b", "c"]
// done true ["a", "b", "c"]

// Synchronous with early abort.
forEach(["a", "b", "c"], function(item, index, arr) {
  console.log("each", item, index, arr);
  if (item === "b") { return false; }
}, allDone);
// logs:
// each a 0 ["a", "b", "c"]
// each b 1 ["a", "b", "c"]
// done false ["a", "b", "c"]

// Asynchronous.
forEach(["a", "b", "c"], function(item, index, arr) {
  console.log("each", item, index, arr);
  var done = this.async();
  setTimeout(function() {
    done();
  }, 500);
}, allDone);
// logs:
// each a 0 ["a", "b", "c"]
// each b 1 ["a", "b", "c"]
// each c 2 ["a", "b", "c"]
// done true ["a", "b", "c"]

// Asynchronous with early abort.
forEach(["a", "b", "c"], function(item, index, arr) {
  console.log("each", item, index, arr);
  var done = this.async();
  setTimeout(function() {
    done(item !== "b");
  }, 500);
}, allDone);
// logs:
// each a 0 ["a", "b", "c"]
// each b 1 ["a", "b", "c"]
// done false ["a", "b", "c"]

// Not actually asynchronous.
forEach(["a", "b", "c"], function(item, index, arr) {
  console.log("each", item, index, arr);
  var done = this.async()
  done();
}, allDone);
// logs:
// each a 0 ["a", "b", "c"]
// each b 1 ["a", "b", "c"]
// each c 2 ["a", "b", "c"]
// done true ["a", "b", "c"]

// Not actually asynchronous with early abort.
forEach(["a", "b", "c"], function(item, index, arr) {
  console.log("each", item, index, arr);
  var done = this.async();
  done(item !== "b");
}, allDone);
// logs:
// each a 0 ["a", "b", "c"]
// each b 1 ["a", "b", "c"]
// done false ["a", "b", "c"]

Contributing

In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint and test your code using grunt.

Also, please don't edit files in the "dist" subdirectory as they are generated via grunt. You'll find source code in the "lib" subdirectory!

Release History

11/11/2011 v0.1.0 Initial Release.

11/11/2011 v0.1.1 Refactored code to be much simpler. Yay for unit tests!

11/17/2011 v0.1.2 Adding sparse array support. Invalid length properties are now sanitized. This closes issue #1 (like a boss).

License

Copyright (c) 2012 "Cowboy" Ben Alman
Licensed under the MIT license.
http://benalman.com/about/license/