Mummet-core

Mummet is an immutable helper library that tracks dictionary changes. It is optimized for use for Redux, but can be used with any code that needs to track object changes.

By wrapping objects in a tracked layer, you can easily get the current state of each object and compare it with its original "underlying" state.

Mummet also has tracks a "loaded" state for each object, that makes it easy to track the state of objects when they were displayed, useful for example when you need to refresh a filtered page and don't want newly edited objects to disappear just because the filtered keyword was edited.

Installation

npm install --save mummet-core

API usage

Create an empty state, for example in the reducers initialState.

import { track, Dictionary } from 'mummet-core'

interface MyEntity {
    id: number,
    name: string,
    //...etc
}

let state: Dictionary<MyEntity> = {}

Add a tracked object as unmodified

Inserts an object with current and underlying values the same.

With the library...

const entity5: MyEntity = { id: 5, name: 'entity 5' }
state = addOrReplace(state, entity5, 'id')

... or semi-manually

const entity6: MyEntity = { id: 6, name: 'entity 6' }
state = { ...state, [entity6.id]: tracked(entity) }

Inserts a new object without underlying value

const newEntity: MyEntity = { id:7, name: 'newEntity' }
state = addOrUpdate(state, newEntity, 'id')

Update the current name of a tracked object

state = update(state, 5, e => ({...e, name: 'updated entity 5' }))

Update the underlying entity without affecting current changes

This replaces the underlying entity. It also updates all current properties that were unmodified. Thus pending user-changes are kept.

const serverChangedEntity: MyEntity = { id: 6, name: 'server changed name' }
state = setUnderlying(state, serverChangedEntity, 'id')

Find all modified objects

const modified = findModified(state)
const currentList = modified.map(t => t.current)
const originalList = modified.map(t => t.underlying)

Delete an object

state = remove(state, 6)

Find original state of deleted objects

const originalList = findRemoved(state)

Commit one or more modified or deleted object

Assigns the current value to the underlying. Removed objects are excavated from the dictionary at this point.

state = commit(state, [5, 6])

Restore one or more modified or deleted object

Assigns the underlying value to the current. Newly created objects are excavated from the dictionary at this point.

state = rollback(state, [5, 6])

Filter the dictionary based on tracked properties

const trackedList = find(state, e => e.current?.name === 'entity 5' || e.underlying.name === 'entity 6')

API methods ordered by intent

Server actions

addOrReplace(state, entity, id_field_name)

Starts tracking the entity, replacing any existing version in the state, making the entity considered unmodified.

Use this method when the server returns the complete entity state when the user saves his changes.

Note: When tracking the initial state from the server, this call is more effective than calling setUnderlying(), since it doesn't have to check if the object already exists.

setUnderlying(state, entity[], id_field_name)

Updates an existing entity with latest changes from the server, without overwriting uncommitted user changes to the current state.

New entities are added to the state as unmodified.

User actions

addOrUpdate(state, entity, id_field_name)

Completely replaces the current state of an entity without affecting the underlying state.

New entities are added to the state as new.

update(state, id, (previous_state) => next_state)

Makes it easy to replace an entitys current state while inspecting its previous properties.

Note: Make sure to always treat the entity as immutable. Return a new state with {...entity } instead of trying to modify the previous state

updateProperty(state, id, property, value)

Fast method for updating a specific property of an entity while keeping all other properties unchanged.

remove(state, id)

Flags an entity as deleted. It is still possible to rollback() until committed.

refreshLoaded(state)

Resets all loaded states for entities to their current counterparts.

This method should typically be called when the user starts a new search, so it is easy to repeatedly filter entities by their state at the time of the search.

Save actions

commit(state, id[])

Copies the current state of entities to their underlying counterparts. This should be called when changes are submitted to the server.

rollback(state, id, underlying, previous?)

Reverts the underlying state of an entity without affecting its current state. Conditionally this method checks that the current state is still previous.

You can effectively use commit() and rollback() in concert, to make a slow async save operation seem much faster.

1. Store a local copy of the tracked entity.
2. Call commit() to make it appear as saved.
3. Call the async save-method and await its response.
4. Check if the save succeeded, else rollback() the entity to its previous state.

Filter actions

findModified(state)

Returns a list of new or modified tracked entities, but not deleted.

findRemoved(state)

Returns a list of underlying states for deleted entities.

find(state, (trackedEntity) => boolean)

Returns tracked entities that fulfill a custom filter expression.

Note: Since filtered entities can be deleted, the current state must be tested for null before being used in the filter expression.