groups

Organize asynchronous code with groups

Installation

Available in npm

$ npm install groups

Description

Groups is a lightweight library to help organize asynchronous code. It allows you to group related asynchronous callbacks, then notifies you when the entire group is done.

API

Groups

To use Groups require('groups')([options]). This returns a factory for creating groups.

• options Object with the following properties
  • timeout (optional, default: false - no timeout) timeout in millis for any group created by this factory
  • logger (optional, default: console) custom logger to output warnings

Groups.newGroup()

Creates a new Group

Group

Object that can wrap asynchronous callbacks and other groups together.

Each group is an EventEmitter with the following event:

Event: done

function(errors)

The group completed. If there were errors, an array of errors will be passed as the argument - If this group is not monitoring anything (because everything has completed or nothing has been bound to this group), when a listener is added for the done event, it will be emitted immediately.

Methods

The group object exposes a bind method that can be called with a variety of parameters to support a number of asynchronous error handling styles. options is an object that supports a single property thisArg to use when invoking the bound function

group.bind(function(error, result){}, [options])

Error Argument (AKA Node callback)

Similar to Object.bind this method returns a new function that will call the original function^*. The group will monitor this new function for invocations. If the first argument is truthy, it will be treated as an error. An exception is treated like an error.

Example

var group = require('groups').newGroup();

asyncFn = group.bind(function() {
    console.log('I was called')
});

group.once('done', function() {
    console.log('Group is done');
});
setTimeout(asyncFn)

group.bind(function(...){}, null|undefined, [options])

Exception only (AKA no error handling)

Similar to Object.bind this method returns a new function that calls the original function^*. The group will monitor this new function for invocations. Because there is no error handler, exceptions are the only thing that will be treated as an error when the new function is called^**.

Example

var group = require('groups').newGroup();

asyncFn = group.bind(function() { console.log('I was called')}, null);
asyncFn2 = group.bind(function() { console.log('Name is %s', this.name);}, null, {thisArg: {name: 'my name'}});

group.once('done', function() {
    console.log('Group is done');
});
setTimeout(asyncFn)
setTimeout(asyncFn2)

group.bind(group)

Returns the same group. The bound group will be monitored for completion, and if it completes with an error, the monitoring group will complete with an error.

Example

var group = require('groups').newGroup(),
    group2 = require('groups').newGroup();

group.bind(group2);

group.once('done', function() {
    console.log('Group is done');
});
group2.once('done', function() {
    console.log('Group 2 is done');
});

group.bind(function success(...){}, function failure(...){}, [options])

Returns an object { success: function(){}, failure: function(){} } each function will notify the group when it is invoked. The group will complete with an error if the failure function is called, or if an exception is thrown in the success function.

Example

var group = require('groups').newGroup(),
    handlers = group.bind(function success(){}, function failure(){});

group.once('done', function() {
    console.log('Group is done');
});

somefunction(handlers.success, handlers.failure)

^*A bound function can only be called once. All other invocations are considered a noop (in reality, they actually log a warning).

^**When using no error handling, it is not recommended to set a timeout on the group. This is because there is no reliable way to pass along the timeout error. In this situation, if the group times out, the callback will be invoked with the timeout error as the only argument.