eventmonitor

Overview

eventmonitor is a simple JavaScript module for managing dependencies asynchronously by allowing functions to be triggered once their defined prereqs have been satisified.

This makes it easy to build non-blocking code without complex callback nesting, and also to tie a function's execution to multiple, independent preconditions.

To make something trackable, simply announce an event:

    EVENT_MONITOR.announce('MY_EVENT');

Then create connectors to tie a given follower function's execution to one or more prereqs:

    EVENT_MONITOR.connect(['MY_EVENT'], my_follower_func);

This is somewhat similar to a pub/sub model. However, completed events are reevaluated each time either an event is announced or a connector created, meaning that connectors can be instantiated even after their prereqs have occurred and will still trigger their followers.

Usage

1. Define your functions, announcing significant events.

    function a () {
         console.log('a');
         EVENT_MONITOR.announce('A');
    }
    function b () {
         console.log('b');
         EVENT_MONITOR.announce('B');
    }
    function c () {
         console.log('c');
         EVENT_MONITOR.announce('C');
    }
   

2. Connect them to prerequisite events.

    // Make sure C is called after A and B.
    EVENT_MONITOR.connect(['A', 'B'], c);
   

3. Let the event monitor call them.

Complete Syntax

    // Announce event
    EVENT_MONITOR.announce(event, {data_map});
    
    // Create connector
    EVENT_MONITOR.connect([prereq_arr], follower_fn, [args_arr], label);
    
    // Directly provide data to event monitor
    EVENT_MONITOR.provide(key, value);
    
    // Enable logging
    EVENT_MONITOR.debug = true;

Notes

1. Any arguments in the args_arr parameter will be passed to the follower function; this parameter may be omitted if the function does not take arguments.

2. Although data may be provided to via the provide function, it's more useful to send the data_map when announcing an event. When a connector's follower function is executed, event monitor will substitute items in the connector's args_arr with the latest data which has been provided to it, if available.

3. Connector names are completely optional but may be useful for tracing a certain sequence of events.