easy-async

easy-async is a library that helps coordinate asynchronous tasks, similar to Promises and async.js.

Like Promises, you get a "control object" that wraps an asynchronous task. The control object allows you to declare what to do after (or at the same time) as the wrapped task.

Like async.js, easy-async will NOT attempt to plumb arguments through your tasks. Also like async.js, the tasks will fail fast if any task produces an error.

Examples

You can see the examples together in a script here

Tasks receive only one parameter, the callback provided by easy-async. Each task must call the callback, and easy-async will only look for one single argument and assume it's an error.

var exampleTask = function(callback){
  console.log('starting task');
  setTimeout(function(){
    console.log('done with task');
    callback();
  }, 1000);
}

var exampleErrorTask = function(callback){
  console.log('starting task');
  setTimeout(function(){
    callback(new Error('BOOM!'));
  }, 1000);
};

To run through tasks in series, get the control object with 'start', then line up tasks with the 'thenStart' method on the control object:

easyAsync.start(exampleTask)
.thenStart(exampleTask)
.thenStart(exampleTask)
.thenStart(function() {
  console.log('continuing after tasks in series');
});

To run tasks in parallel, use the 'andStart' method on the control object:

easyAsync.start(exampleTask)
.andStart(exampleTask)
.andStart(exampleTask)
.thenStart(function() {
  console.log('continuing after tasks in parallel');
});

To attach an error handler, use the 'onError' method on the control object:

easyAsync.start(exampleTask)
.andStart(exampleTask)
.andStart(exampleErrorTask)
.thenStart(function() {
  console.log('continuing after risky work');
})
.onError(function(err){
  console.log('error handler received an error');
  console.error(err);
});

API

The easy-fix module exports only one method: start. The start method returns the "control object" (kind of like a promise) which contains the other methods listed here.

start(callback, options)

Create and return the control object, and start the callback task. The control object has the other methods listed here. The options are the same as thenStart and andStart methods (listed below). As a convenience, the callback can be null.

The callback is called with exactly one argument (a callback) which it must call to continue the easy-fix asynchronous task execution.

thenStart(callback, options)

Run the callback after all previous callbacks to thenStart and andStart have completed. Use this to declare tasks to run in series.

The callback is called with exactly one argument (a callback) which it must call to continue the easy-fix asynchronous task execution.

andStart(callback, options)

Run the callback in parallel with a previous callback from thenStart, as well as any other other callbacks from successive calls to andStart. Use this to declare tasks to execute in parallel.

The callback is called with exactly one argument (a callback) which it must call to continue the easy-fix asynchronous task execution.

onError(callback)

Specify a custom error handler. The default error handler simply throws the error.

The error handler callback is called with two arguments: (error, errorIndex).

The error is the same error that was passed in to any task callback or caught by a try/catch block (when wrapWithTry is specified as an option).

The errorIndex is a count (starting at 1) of all errors encountered by this control object. As an example use case, easy-async may be used to coordinate multiple tasks in parallel when preparing a response to a single web request. Several of the tasks may generate errors - and the errorIndex may be used to guarantee that the error handler will only attempt to respond once to that web request.

changeDefaults(options)

Specify new default options, which apply to all futher tasks added with thenStart and andStart.

Options

Options can be specified per-task, or by calling the changeDefaults method.

• wrapWithTry - If true, tasks will be wrapped in a try/catch block, and caught errors passed through the onError handler. Default is false.
• onError - specify a custom error handler. The default error handler simply throws the error.

Stay up to date

As of June 2016, the new easy-async v1 has some very prudent breaking changes (and new features)! Please read the change log!