Trigger

Custom JavaScript event system. There is a svelte-specific version @seihoukei/trigger-svelte.

Usage

You set up handlers for arbitrary triggers and then can trigger them. Both handlers and trigger activations can have any number of arguments. Handler arguments are passed to callback before trigger arguments.

Set up handlers

Any valid Map key can be a trigger. There are several ways to set up a handler.

There are two types of handlers:

• Normal - executes with given arguments and might return a value. Called with handler(...handlerArguments, ...triggerArguments)
• Modifier - executed with input value in addition to arguments and returns modified value. Called with handler(input, ...handlerArguments, ...triggerArguments)

Normal handlers are set up with Trigger.createHandler(trigger, handler, ...args) or Trigger.on(trigger, handler, ...args)

Modifying handlers are set up with Trigger.createModifier(trigger, handler, ...args)

You can cancel either with .cancel() method of returned value.

Triggering events

Plain execution

Use Trigger(trigger, ...args) to execute normal handlers set up for given trigger. This is similar to array.forEach

Polling results

Use Trigger.poll(trigger, ...args) to execute normal handlers set up for given trigger and collect execution results. This is similar to array.map

Value modifications

Use Trigger.modify(input, trigger, ...args) to execute modifier handlers set up for the trigger in a chain. This is similar to array.reduce.

Miscellaneous

Trigger.createTrigger() returns function that executes triggers with itself as a key. Trigger.createPoll() and Trigger.createModification() create similar functions for polling and modification.

Trigger.clearTrigger(trigger) removes all handlers associated with event and removes entry for it from storage.

Quick example

function counterCallback(handlerArgument, triggerArgument) {
    console.log(`${handlerArgument} + ${triggerArgument} = ${handlerArgument + triggerArgument}`)
    return handlerArgument + triggerArgument
}

// Set up handlers
const handlers = [
    Trigger.on("count", counterCallback, 1),
    Trigger.on("count", counterCallback, 2),
    Trigger.createModifier("boost", x => x + 1).setPriority(1),
    Trigger.createModifier("boost", x => x * 2).setPriority(0),
]

Trigger("count", 3)
//1 + 3 = 4
//2 + 3 = 5

console.log(Trigger.poll("count", 4))
//1 + 4 = 5
//2 + 4 = 6
//[5, 6]

console.log(Trigger.modify(5, "boost"))
//11

// Clean up handlers
handlers.forEach(handler => handler.cancel())

console.log(Trigger.poll("count", 6))
//[]

console.log(Trigger.modify(7, "boost"))
//7