object-viewer

View and listen for changes on state object that keeps track of saved vs patched state.

Example

var Viewer = require('object-viewer')
var assert = require('assert')

var base = {
  person: {
    kara: {name: 'Kara Thrace'},
    lee: {name: 'Lee Adama'}
  },
  ship: {
    galactica: {type: 'battlestar', number: 75},
    pegasus: {type: 'battlestar', number: 62}
  }
}
var viewer = Viewer(base)

viewer.on('change', function() {
  // access state via viewer.{base,patched,patch}
})

// the contents of the 'people' array
assert.deepEqual(viewer.read('person'), [
  {
    key: 'kara',
    value: {name: 'Kara Thrace'}
  },
  {
    key: 'lee',
    value: {name: 'Lee Adama'}
  }
])

// set value at key path
viewer.set('person', 'd', {name: 'Anastasia Dualla'})
// will fire a 'change' event
// see tests for more examples

Concept Overview

This is an attempt to provide a general, familiar interface to large, nested/namespaced, state objects that need to:

• be modified and know the difference between the original state and the modified state
• emit events when they've been changed
• allow changes to the base state without modifying the patch

An instance of object-viewer keeps track of 3 states:

1. base The original state
2. patched The state after changes have been made
3. patch The difference between the two states

The getters get and read can view any of these states by setting opts.view to the desired state. The setter is necessary to trigger events and update the patch.

Methods

var viewer = Viewer(base={}, patch={})

base is the state to diff against when determining what has changed. patch is a patch from patcher that is used to as the initial set of changes to the base state.

viewer.read(keyPath..., opts={})

Get an array of objects at the given key path in the format {key: '<key>', value: '<value>'} (the same format used by levelup).

• opts.view = 'patched' Set which view of the state to read. options are patched, base, and patch.

viewer.get(keyPath..., opts={})

Gets the value at the given key path. opts behaves the same as in read.

viewer.set(keyPath..., value)

Gets the value at the given key path to value. set values are always set on the patch. To modify the base state, use setBase.

viewer.setBase(base={})

Sets the base state. Does not influence the patch.

viewer.applyPatch(patch={})

Applies the given patcher patch to the existing patch. Does not modify the base state.

Events

viewer.on('base', fn())

Emitted when a new base is set. Also fires when an instance is created.

viewer.on('patch', fn())

Emitted when a new patch is applied. Also fires when an instance is created.

viewer.on('change', fn())

Emitted when any value is set.

License

MIT