Description

This is one of the core libraries used in ScadaJS for managing events, timeouts and signalling between flow branches.

In a process flow, a condition may need to .wait for an external signal from another function's callback, from another process or from another network device.

button-press = new Signal

queue.on-receive = (msg) ->
    button-press.go err=null, msg.data.index

...

do-something!
do-something-else!
err, button-num <~ button-press.wait
console.log "Button number #{button-num} is pressed!"

Signal

signal = new Signal

signal.wait [timeout,] callback(err, ...args)  # Waits for `signal.go` to call the `callback`.

...

signal.go err, ...args

Reusable signals

If you want to declare .wait handler once and use the same handler over and over again, create your Signal instance with {reusable: yes} option:

signal = new Signal {+reusable}

signal.wait [timeout,] callback(err, ...args)  # Waits for `signal.go` to call the `callback`.

...

on-some-condition -> 
    signal.heartbeat! # this will re-set the signal

SignalBranch

When .joined, returns overall error and branch signals

branch = new SignalBranch {timeout?}

for myArray
    signal = branch.add!  # adds a new signal to the branch
    # or with a 1 second timeout:
    # signal = branch.add 1000ms
    ...
    # do something async here
    err, res <~ some-async-operation
    # do something with result
    signal.go err

err, signals <~ branch.joined
# all async operations are finished at this point.

branch.cancel!: Cancels the execution and properly cleans up the code registered by/after branch.joined.

err : The error either set by

• SignalBranch's master timeout or
• any of branch signals, either by
  • Signal's timeout (defined by branch.add timeout) or
  • by .go method's err argument

signals : Array of that branch's Signal instances where each instance has at least error and response[] properties.

CDN

https://cdn.jsdelivr.net/gh/ceremcem/signal@v0.4/dist/signal.js

Example

In the following example, "hello" output waits for both signals to be emitted:

Ractive Playground