Relaks Event Emitter

Relaks Event Emitter is the base class of data sources used by Relaks applications. It's designed for promised-based asynchronous code. It provides a notable feature allowing event listeners to postpone the default action associated with an event.

Methods of emitter

• addEventListener
• removeEventListener
• triggerEvent
• waitForEvent

addEventListener

function addEventListener(name: string, handler: function, beginning?:boolean): void

Add an event listener. If beginning is true, then handler will receive the event prior to handlers added previously. Otherwise it's placed at the end of the queue.

removeEventListener

function removeEventListener(name: string, handler: function): void

Remove an event listener.

waitForEvent()

async function waitForEvent(type: string): Event

Return a promise that is fulfilled when an event of the specified type occurs.

triggerEvent

function triggerEvent(evt: object): boolean

Send an event object to any listeners interested in the event. A method used by the event emitter itself. The return value indicates whether there were any listeners.

Methods of event object

• preventDefault
• postponeDefault
• stopImmediatePropagation
• waitForDecision

preventDefault

function preventDefault(void): void

Indicate that the default action should not be performed.

postponeDefault

function postponeDefault(proceed: Promise): void

function postponeDefault(callback: AsyncFunction): void

Request that the default action to be postponed. The method accepts either a promise or a callback function that returns a promise. An event emitter would wait for this promise to be fulfilled before perform the default action. If the promise's fulfillment value is false (and not merely "falsy"), that'd be the equivalent of calling preventDefault() and stopImmediatePropagation()--i.e. the default action will not occur.

When there are multiple listeners, a call to this method will keep other listeners from receiving the event until the promise given is fulfilled.

stopImmediatePropagation

function stopImmediatePropagation(void): void

Keep listeners further down the chain from receiving this event.

waitForDecision

async function waitForDecision(void): void

A method used by the event emitter itself. If a promise is given to postponeDefault() within an event handler, this method will wait for its fulfillment. The method returns immediately otherwise.