React Sequencer

A better way to do animations in React.

Version 2 now with hooks!

Docs

• Examples (V1)
• Getting Started
• useSequencer

Overview

React sequencer lets you perform complex animations easily by tying them to a time-sequenced set of states. The simplest usage is to implement the useSequencer hook inside your function components, which will give you the sequencer state and an api to control it.

You first define a set of steps for your sequence as tuples of names and durations:

const steps = [['initial', 100], ['middle', 100], ['final', 0]]

Then pass this as configuration to useSequencer:

import { useSequencer } from 'react-sequencer'

const steps = [['initial', 100], ['middle', 100], ['final', 0]]

const MyComponent = props => {
  let [state, api] = useSequencer({ steps })
  return (
    <div>
      <div>The current step: {state.current}</div>
      <button
        onClick={() => {
          api.play()
        }}
      >
        Start
      </button>
    </div>
  )
}

Here state contains the sequencer state and api provides some methods to control the sequencer. When your sequencer starts playing, it runs through the steps and updates the state on every step, passing the current name into state.current.

Allowing you to control your time sequenced events in this way has many benefits:

• Easily add / remove or edit your steps from one place in your code
• Have your sequencer trigger css animations, text changes, or whatever you like
• Every step runs in its own animation frame so no repaint or timeout hacks are needed to get your animations behaving exactly as you like
• Add sequencers to multiple components and guarantee that they update in sync

Getting started

Install from NPM:

npm install react-sequencer

useSequencer()

(options: Options, onBeforeRender: Function) => [SequencerState, SequencerApi]

The useSequencer() hook takes two parameters:

options

options: Options

A configuration object to initialize the sequencer.

onBeforeRender()

onBeforeRender: (api: SequencerApi) => void

A function you pass to update the sequencer in response to a change in props or state. Your function is passed the sequencer api as an argument, allowing you to call play, pause, stop or complete. The advantage of updating the state here is that your state/props and the sequencer state are rendered perfectly in sync, allowing to design animations with precision.

Returns

The hook returns a tuple of a SequencerState and SequencerApi.

Options

Pass options to useSequencer.

Steps

steps: Array<[string, number]>

Pass an array of tuples that defines the steps of the sequence. The first value should be the name of the step, the second the duration in milliseconds.

useSequencer({
  steps: [['initial', 100], ['middle', 100], ['final', 0]]
})

If you specify a duration of 0 for a step, it means that the following step will fire on the next animation frame. This guarantees that every state must be visited and rendered before transitioning to the next state.

This is useful for creating an animation 'set up' state where you may want to prepare some css before an animation begins. You can simply do this without needing to change anything else in your sequence:

const steps = [['pre', 0], ['initial', 100], ['middle', 100], ['final', 0]]

pre becomes the default state when your component mounts, until the sequencer is started, which moves on to initial on the next frame. By defining all the states explicitly in this fashion, it becomes easy to insert steps, change durations, swap steps and understand how your animation behaves.

endMode

endMode: 'end' | 'start' | 'loop'

The end mode determines the behavior of the sequencer once it reaches the end of the last step.

• 'end' (default): The sequencer remains in the last step.
• 'start': The sequencer resets to the first step and becomes idle.
• 'loop': The sequencer resets to the first step and continues looping until stop() or pause() is called.

complete

complete: boolean

If set to true, the sequencer is initialized in the 'completed' state, meaning it is in the final step and idle. It will remain in this state until either play() or stop() is called.

Sequencer State

The sequencer state offers the following properties.

current

current: string

The current step of the sequencer, as specified by the step names provided in the config.

index

index: number

The index of the current step.

isPlaying

isPlaying: boolean

true if the sequencer is playing.

isComplete

isComplete: boolean

true if the sequencer has finished sequencing through the steps and is idle. endMode must be set to end in order to reach this state.

isStopped

isStopped: boolean

true if the sequencer is in its first step and not playing.

Sequencer Api

isBefore()

isBefore(name: string): boolean

true if the sequencer has not yet reached the step with the provided name.

isAfter()

isAfter(name: string): boolean

true if the sequencer has passed the step with the provided name.

play()

play(): void

Starts the sequencer, or continues playing if the sequencer was paused.

pause()

pause(): void

Pauses the sequencer. The sequencer tracks how far it is through the current step by the millisecond so that playback continues from the same moment.

stop()

stop(): void

Stops playback and resets the sequencer back to the first step.

complete()

complete(): void

Stops playback and puts the sequencer to the end of the final step.