state-eventer

Read and write values to a state object and listen for changes at any given path

Install

npm i state-eventer

Example

// initialize an empty state
const state = new StateEventer()
state.get() // {}

// listen for state changes at specific paths
const listeners = [
  state.on('books', console.log),
  state.on('books.1', console.log)
]

// remove listener
listeners[0].off()

// add/modify value and notify listeners
state.set('books.1.title', 'War and Peace')

// retrieve values from the state
state.get()                // { books: { 1: { title: 'War and Peace' } } }
state.get('books')         // { 1: { title: 'War and Peace' } }
state.get('books.1')       // { title: 'War and Peace' }
state.get('books.1.title') // 'War and Peace'

// remove values from the state and notify listeners
state.unset('books.1.title')
state.get('books.1.title') // undefined

// reset the entire state and notify listeners
state.set({})
state.get() // {}

// transform
state.update('counter', n => n + 1, 0) // 1

Methods

StateEventer

on( path, listenerFn )

• path (String|Array) the path to listen for changes
• listenerFn (Function) the function to call when the value changes

Returns Listener (see below)

get( path, [defaultValue] )

• path (String|Array) the path of the desired value
• defaultValue (*) optional default value to return if the value at the specified path is undefined

set( path, value )

• path (String|Array) the path at which to set the value
• value the value to set

set( value )

• value (Object) resets the root state to this value

unset( path )

• path (String|Array) removes this path from the state

update( path, transformFn, [defaultValue] )

• path (String|Array) the path at which to set the value
• transformFn (Function) transform the current value to a new value
• defaultValue (*) optional default value to pass into the transform function if the value at the given path is undefined

  update('counter', n => n + 1, 0)
  

Listener

off() removes the listener

License

MIT