short-signal

short-signal

short-signal is a lightweight version of js-signals which is heavily inspired by Robert Penner’s AS3-Signals. Signal is an alternative to Events/Promises/Callbacks. To know more about the differences, you can check out the Wiki page of js-signals.

Unlike other trimmed version js-signals, short-signal preserves some useful features like priorty and arguments injection which comes in handy during the development.

Dispatch the same signal within the signal callback is not recommended. If it happens the new signal execution will kick in and stop the unfinished execution.

Examples

Basic Example

Example of using the basic functions: add(), dispatch() and remove() with short-signal

var onStarted = new ShortSignal();

function callback(param1, param2) {
    console.log(param1 + ' ' + param2);
}

onStarted.add(callback); // add listener
onStarted.dispatch('foo', 'bar'); // dispatch signal passing custom parameters
onStarted.remove(callback); // remove a signle listener

addOnce()

If you the callback to be dispatched only once, you can use addOnce().

var onStarted = new ShortSignal();

function callback() {
    console.log('hello');
}

onStarted.addOnce(callback);
onStarted.dispatch(); // log : hello
onStarted.dispatch(); // do nothing

Priority

The first argument of the add() and addOnce() is the priority, the higher it is, the earlier it will be dispatched. The default value is 0, and order by first comes first served principle.

var onStarted = new ShortSignal();

function callback1() {
    console.log('1');
}

function callback2() {
    console.log('1');
}

function callback3() {
    console.log('3');
}

onStarted.add(callback1);
onStarted.add(callback2);
onStarted.add(callback3, null, 10);
onStarted.dispatch(); // log : 3, 1, 2

Context

Like function binding, you can provide the context for the callback binding. Same context with the same function will be ignored.

var onStarted = new ShortSignal();

function callback() {
    console.log(this.id);
}

var a = {id: 'a'};
var b = {id: 'b'};

onStarted.add(callback, a);
onStarted.add(callback, a);
onStarted.add(callback, b);
onStarted.dispatch(); // log : a, b

Argument prefix

You can also add argument prefix with the add() and addOnce() like in Function.bind(). One thing you need to keep in mind is that, for the duplicated callback checking, it only checks the funtion and the context, same function with the same context with new argument prefix will be rejected instead of overridden.

var onStarted = new ShortSignal();

function callback(param1, param2, param3, param4) {
    console.log(param1 + param2 + param3 + param4);
}
onStarted.add(callback, null, 0, 'a', 'b');
onStarted.dispatch('c', 'd'); // log : abcd

Stop Propagation

You can stop propagation by returning false in the callback function. By stopping propagation, in the dispatch() call it will return the listener which triggered the stop propagation.

var onStarted = new ShortSignal();

onStarted.add(function(){
	return false; // returns "false" to stop propagation
});
onStarted.add(function(){
	console.log('wont be triggered'); // this function won't be trigger
});
onStarted.dispatch(); // log : {...} // will return the listener that stopped the propagation

Installation

Manually

Download short-signal here.

Npm

Check out the npm page here.

Testing

run npm run test to run the test suite.

TODO

• additional features?
• add more tests