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EZ Web Audio / Sequence

Class: Sequence ​

Defined in: packages/core/src/sequence.ts:70

Sequence schedules arbitrary callbacks at musical time positions tied to a Transport.

Events are stored as beat positions (not seconds) so that live BPM changes automatically affect subsequent event scheduling without re-scheduling. Sequences follow the Transport lifecycle: they play when the Transport plays, pause when it pauses, and reset when it stops.

Example ​

typescript
import { createTransport, createSequence, createSound } from 'ez-web-audio'

const transport = await createTransport({ bpm: 120, timeSignature: [4, 4] })
const kick = await createSound('kick.mp3')

const seq = createSequence(transport, { length: '4m' })

// Schedule kick on beat 1 of each bar
seq.at('1:1:0', (time) => kick.playIn(time - ctx.currentTime))
seq.at('2:1:0', (time) => kick.playIn(time - ctx.currentTime))
seq.at('3:1:0', (time) => kick.playIn(time - ctx.currentTime))
seq.at('4:1:0', (time) => kick.playIn(time - ctx.currentTime))

transport.start() // Events fire at correct musical positions

// Change BPM — events automatically adjust timing
transport.bpm = 140

Extends ​

Constructors ​

Constructor ​

new Sequence(transport, options): Sequence

Defined in: packages/core/src/sequence.ts:99

Parameters ​

transport ​

Transport

options ​

SequenceOptions

Returns ​

Sequence

Overrides ​

TypedEventEmitter.constructor

Accessors ​

length ​

Get Signature ​

get length(): number

Defined in: packages/core/src/sequence.ts:135

Length of the sequence in beats.

Returns ​

number

loop ​

Get Signature ​

get loop(): boolean

Defined in: packages/core/src/sequence.ts:130

Whether this sequence loops.

Returns ​

boolean

Methods ​

_clearListeners() ​

protected _clearListeners(): void

Defined in: packages/core/src/events/typed-event-emitter.ts:192

Remove every listener registered through this emitter (via addEventListener(), on(), or once()), regardless of how many or what event type they're bound to.

Native EventTarget has no removeAllListeners(). This works around that by aborting a shared AbortSignal threaded through every addEventListener() call this class makes, then swapping in a fresh AbortController so the instance can keep accepting new listeners afterward (e.g. if it's reused before being garbage collected).

Subclasses call this from their dispose() alongside neutering dispatchEvent — the neuter stops future emits, this stops stale listener closures from being retained/invoked at all.

Returns ​

void

Inherited from ​

TypedEventEmitter._clearListeners

addEventListener() ​

Call Signature ​

addEventListener<K>(type, listener, options?): void

Defined in: packages/core/src/events/typed-event-emitter.ts:44

Add a typed event listener for known event types. Overloaded to provide type safety for known event types while remaining compatible with the native EventTarget API.

Type Parameters ​
K ​

K extends "event" | "loop"

Parameters ​
type ​

K

The event type (key of TMap)

listener ​

(event) => void

Typed event handler

options? ​

Standard addEventListener options

boolean | AddEventListenerOptions

Returns ​

void

Inherited from ​

TypedEventEmitter.addEventListener

Call Signature ​

addEventListener(type, listener, options?): void

Defined in: packages/core/src/events/typed-event-emitter.ts:49

Add a typed event listener for known event types. Overloaded to provide type safety for known event types while remaining compatible with the native EventTarget API.

Parameters ​
type ​

string

The event type (key of TMap)

listener ​

Typed event handler

EventListenerOrEventListenerObject | null

options? ​

Standard addEventListener options

boolean | AddEventListenerOptions

Returns ​

void

Inherited from ​

TypedEventEmitter.addEventListener

at() ​

at(time, callback): string

Defined in: packages/core/src/sequence.ts:153

Schedule a callback at a musical time position.

Parameters ​

time ​

MusicalTimeNotation

Musical time notation (e.g., '4n', '2:1:0') or beats

callback ​

SequenceCallback

Function to call when the event fires

Returns ​

string

Event ID for later removal via .remove()

Example ​

typescript
const id = seq.at('4n', (time, pos) => {
  console.log(`Event at bar ${pos.bar}, beat ${pos.beat}`)
})

clear() ​

clear(): void

Defined in: packages/core/src/sequence.ts:196

Remove all scheduled events.

Returns ​

void

dispose() ​

dispose(): void

Defined in: packages/core/src/sequence.ts:427

Dispose the Sequence, unregistering from Transport and releasing resources. After disposal, the Sequence should not be used.

Returns ​

void

emit() ​

protected emit<K>(type, detail): void

Defined in: packages/core/src/events/typed-event-emitter.ts:95

Emit a typed event with the given detail.

Creates a CustomEvent with the provided detail and dispatches it on this target. Subclasses call this internally to fire lifecycle events.

Type Parameters ​

K ​

K extends "event" | "loop"

Parameters ​

type ​

K

The event type to emit (key of TMap)

detail ​

SequenceEventMap[K]["detail"]

The event detail object (typed by TMap)

Returns ​

void

Inherited from ​

TypedEventEmitter.emit

off() ​

off<K>(type, listener): this

Defined in: packages/core/src/events/typed-event-emitter.ts:167

Unsubscribe from an event.

Note: Due to native EventTarget limitations, you must provide the same listener function reference that was used when subscribing.

Type Parameters ​

K ​

K extends "event" | "loop"

Parameters ​

type ​

K

The event type to unsubscribe from

listener ​

(event) => void

The event handler function to remove

Returns ​

this

this for chaining

Example ​

typescript
const handler = (e) => console.log(e.detail)
emitter.on('play', handler)
// later...
emitter.off('play', handler)

Inherited from ​

TypedEventEmitter.off

on() ​

on<K>(type, listener): this

Defined in: packages/core/src/events/typed-event-emitter.ts:116

Subscribe to one or more events. Supports chaining.

Type Parameters ​

K ​

K extends "event" | "loop"

Parameters ​

type ​

The event type(s) to subscribe to (key or array of keys of TMap)

K | K[]

listener ​

(event) => void

The event handler function

Returns ​

this

this for chaining

Example ​

typescript
emitter.on('play', handlePlay).on('stop', handleStop)
emitter.on(['play', 'stop'], handleBoth)

Inherited from ​

TypedEventEmitter.on

once() ​

once<K>(type, listener): this

Defined in: packages/core/src/events/typed-event-emitter.ts:141

Subscribe to an event once. Handler is removed after first invocation.

Type Parameters ​

K ​

K extends "event" | "loop"

Parameters ​

type ​

K

The event type to subscribe to

listener ​

(event) => void

The event handler function

Returns ​

this

this for chaining

Example ​

typescript
emitter.once('end', () => console.log('Finished'))

Inherited from ​

TypedEventEmitter.once

remove() ​

remove(id): boolean

Defined in: packages/core/src/sequence.ts:185

Remove a previously scheduled event by its ID.

Parameters ​

id ​

string

Event ID returned by .at()

Returns ​

boolean

true if the event was found and removed

removeEventListener() ​

Call Signature ​

removeEventListener<K>(type, listener, options?): void

Defined in: packages/core/src/events/typed-event-emitter.ts:70

Remove a typed event listener for known event types. Overloaded to provide type safety for known event types while remaining compatible with the native EventTarget API.

Type Parameters ​
K ​

K extends "event" | "loop"

Parameters ​
type ​

K

The event type (key of TMap)

listener ​

(event) => void

Typed event handler to remove

options? ​

Standard removeEventListener options

boolean | EventListenerOptions

Returns ​

void

Inherited from ​

TypedEventEmitter.removeEventListener

Call Signature ​

removeEventListener(type, listener, options?): void

Defined in: packages/core/src/events/typed-event-emitter.ts:75

Remove a typed event listener for known event types. Overloaded to provide type safety for known event types while remaining compatible with the native EventTarget API.

Parameters ​
type ​

string

The event type (key of TMap)

listener ​

Typed event handler to remove

EventListenerOrEventListenerObject | null

options? ​

Standard removeEventListener options

boolean | EventListenerOptions

Returns ​

void

Inherited from ​

TypedEventEmitter.removeEventListener