The Great Mutator

Describe mutations, get results! With batching and a change log.

The great mutator is an wrapper around a state tree. It could be called a store. It's really an object.

You can use this wrapper to describe mutations that will be staged until applied as a single change.

Choose your backing structure:

import theGreatMutator from 'the-great-mutator';

And create a great mutator.

const initialState = {
  top: 'level',
  such: {
    nested: 'wow'
  },
  array: [{id: 1. prop: true}],
  counter: 0
};

const state = theGreatMutator(initialState);

Mutating

With this wrapper you can send in your mutations, like this:

state.mutate({ top: 'changed' });
state.get('top'); //level

Except that our state has not changed yet. It's only staged.

state.applyPendingMerges();
state.get('top'); //changed

This also works:

state.mutate(['such.nested', 'very'])
state.get('such.nested'); //wow
state.applyPendingMerges();
state.get('such.nested'); //very

And you can apply multiple mutations at once. Using any of the given syntax.

state.mutate([
  ['such.nested', 'very'],
  [{top: 'changed' }]
]);

It can handle modifying arrays in clever ways:

// This replaces the existing value of 'array'
state.mutate(['array', [1,2,3,4]]);

// This pushes a record onto the array
state.mutate(['array+', { this: 'element', is: 'pushed', onto: 'the', array: true }]);

// This replaces the element with the matching id.
state.mutate(['array!', { id:1, prop: false }]);

// While this only modifies what is passed in.
state.mutate(['array:4', { prop: false }])

// And you could have done this:
state.mutate(['array:4.prop', false])

You can pass in a function:

const increment = (current) => current + 1;

state.mutate(['counter', increment]);
state.get('counter') //1
state.applyPendingMerges();
state.get('counter') //2

But it also considers things that have been staged. So this works too:

state.mutate(['counter', 0]);
state.applyPendingMerges();
state.get('counter') //0

state.mutate(['counter', increment]);
state.mutate(['counter', increment]);
state.mutate(['counter', increment]);
state.get('counter') //0

state.applyPendingMerges();
state.get('counter') //3

As do promises:

state.mutate(['top', Promise.resolve('only applied on resolution and after batching')]);
state.get('top') //changed
state.applyPendingMerges();
state.get('top') //only applied on resolution and after batching

Things you should know

• It won't mutate _id, even if you ask nicely.
• It relies on array elements having an id property.

Reading Values

You can get the root object by asking for all. Or read a specific value using get. Get uses ok-selector under the hood so you can use dot.strings.to.state as well as reference.arrays:1.items.

state.all();
state.get('path.to.some.state');

Getting the changes

The flushChanges method returns an array of changes as well as emptying out the change array. Changes are the result of applyPendingMerges calls.

state.mutate(['counter', 0]);
state.flushChanges() // []
state.applyPendingMerges();
state.get('counter') //0
state.flushChanges() // [{counter: 0}]

state.mutate(['counter', increment]);
state.mutate(['counter', increment]);
state.mutate(['counter', increment]);
state.flushChanges() // []
state.applyPendingMerges();
state.flushChanges() // [{counter: 3}]

state.mutate(['counter', increment]);
state.applyPendingMerges();
state.mutate(['counter', increment]);
state.applyPendingMerges();
state.mutate(['counter', increment]);
state.applyPendingMerges();
state.flushChanges() // [{counter: 4}, {counter: 5}, {counter: 6}]

Disabling change recording

You can disable recording of changes by passing in configuration option as the second parameter of the great mutator constructor. The flushChanges method always returns an empty array.

const state = theGreatMutator({}, { trackChanges; false });
state.mutate(['counter', increment]);
state.mutate(['counter', increment]);
state.mutate(['counter', increment]);
state.applyPendingMerges();
state.flushChanges() // []