Listen NPM | npm.io

listen.js

A tiny library to wait for the results of multiple callbacks. For node and the browser.

Install

This will install the listen module in your current project and add it to the dependencies:

npm install listen --save

Usage

var listen = require('listen');

var listener = listen();

var callbackA = listener();
var callbackB = listener();

/*
 * Do async stuff with callbacks.
 *
 * Callbacks follow the Node.js convention. They expect an error or null as
 * the first argument and an optional value as the second:
 *
 * Fail: callback(new Error('ouch!'));
 * Return: callback(null, 'some return value');
 */
listener.then(function (err, values) {
  /*
   * err    - 1) null if no callback received an error
   *          2) the error of the callback that received an error
   *          3) an error with name ErrorList wrapping multiple errors
   *
   * values - The non-undefined return values from all callbacks in order of
   *          callback creation, also exposing names callbacks (see API)
   */
});

API

Start with var listen = require('listen'), then use the listen function to create listeners. Use the listeners to create callbacks.

listen([values]): Creates and returns a new listener function. If values are given, it must be an array with initial values.
listener([name][, func][, timeout]): Creates a new callback associated with the listener. Throws if called after then. All arguments are optional and can be combined.
- name exposes the return value of the callback on the values object under that name.
- func gets invoked with (err, value) when the callback is invoked.
- timeout calls the callback with a TimeoutError after the timeout.
listener.then(func): Invokes the given function once all callbacks where invoked. If none of the callbacks had errors, the first argument is null, otherwise it's an Error. The second argument is the values array in order of callback creation. Can only be called once.
listener.push(value): Pushes a value to the internal values array. Throws if called after then.
listener.err(error): Adds an error to the internal error list. Throws if called after then.