Taking snapshots ​

Sometimes it can be useful to take a snapshot of state at a specific point in time for use later. Harlem provides a mechanism for you to take a snapshot of state at a point in time and access that copy of state later or reset the store back to that point in time.

Some common use-cases of snapshots are:

• Custom reset functionality
• Rolling back state if mutations fail (transactions)

To use snapshots simply call the snapshot function on the store at the point you wish to snapshot the state:

export const {
    state,
    getter,
    mutation,
    action,
    snapshot
} = createStore('user', {
    firstName: 'John',
    lastName: 'Smith'
});

const snap = snapshot(); // take a snapshot
snap.apply(); // apply the snapshot when ready

Like to the reset method, the apply method on the snapshot accepts a function argument for specifying a specific part of the snapshot to apply:

snap.apply(state => state.firstName);

The state of the snapshot can also be accessed via the state property on the snapshot:

console.log(snap.state.firstName);