Transaction

A Transaction is an object when applied to a store state can produce a new store state.

Usage

A transaction is created in Actions (a function that returns a transaction).

In the example below the action incrementCounter returns a transaction that increments the counter.

const counterField = key.field(0);
 
// An action is a function that returns a transaction
function incrementCounter(): Transaction {
  const transaction = counterField.update((n) => n + 1);
  return transaction;
}

Updating the store state

You can create transaction by calling incrementCounter() and dispatching it to update the store state.

key.effect((store) => {
  const oldValue = counterField.get(store.state);
  store.dispatch(incrementCounter());
  const newValue = counterField.get(store.state);
  console.log(`counter changed from ${oldValue} to ${newValue}`);
});

See Effect for more information on effects.

Methods

`.step()`

Adds a step to that modifies the store state.

Signature:

transaction.step(stepper: (StoreState) => StoreState)

Arguments:

stepper - A function that takes a store state and returns a new modified store state.

Returns:

The same transaction object.

Example:

function incrementCounter(): Transaction {
  const txn = key.transaction();
 
  return txn.step((storeState) => {
    const counterValue = counterField.get(storeState);
 
    // field.update returns a transaction
    const newTxn = counterField.update(counterValue + 1);
 
    // apply the transaction to the store state to return
    // a new store state.
    return storeState.apply(newTxn);
  });
}

See StoreState.apply() for more information on how to updating the store state.

Store Cleanup