Key

createKey

Signature

createKey(name:string, dependencies?: Slice[])

Arguments:

name - Name of the slice.
dependencies - An optional array of slices that this slice depends on.

Returns:

A Key object.

Example

import { createKey } from '@nalanda/core';
 
const key = createKey('mySlice', [someSlice, someOtherSlice]);

The following methods are available on the key object.

`.derive()`

Creates a new derived field object.

Signature:

key.derive<T>(compute: (storeState: StoreState) => T, options?: DeriveOptions): DerivedField<T>

Arguments:

compute - A function that computes the derived value.
options? - An optional object containing the following options.
- equal - (a: T, b: T) => boolean A comparator function that compares the previous and current value of the derived field. If the comparator returns true, the derived field is not updated. Defaults to Object.is.

Returns:

DerivedField

Example:

const counterField = key.field(0);
const positiveNumberField = key.derive((store) => {
  return counterField.get(state) > 0;
}, {
  equal: (a, b) => a === b,
});

`.effect()`

Creates a new effect object.

Signature:

key.effect(effect: (store: EffectStore) => void | Promise<void>) : string

Arguments:

effect - The callback to run as a side effect. The first argument of this callback is an EffectStore.

Returns:

string - The name of the effect.

Example:

const counter = key.field(0);
 
key.effect((store) => {
  // This will run whenever the counter value changes
  const counterValue = counter.track(store);
  console.log(`The counter value is ${counterValue}`);
});

`.field()`

Creates a new field object.

Signature:

key.field(initialValue: any, options)

Arguments:

initialValue - Initial value of the field.
options:
- equal: (a: T, b: T) => boolean A comparator function that compares the previous and current value of the field. If the comparator returns true, the field is not updated. Defaults to Object.is.

Returns:

StateField

`.slice()`

Creates a new slice object.

Signature:

key.slice({ ...fields, ...actions });

Arguments:

object: An object containing the fields or actions you want to expose externally.

Returns:

Slice

Example:

export const countSlice = key.slice({
  // fields
  count,
  // actions
  increment,
});

Note: Only the slice should be exported from your file.

`.transaction()`

Creates a new transaction object which is used to update the slice state.

Signature:

key.transaction();

Returns:

A transaction object.

Example:

function increment() {
  const txn = key.transaction();
 
  return txn.step((state: StoreState) => {
    return state.apply(count.update((c) => c + 1));
  });
}

EffectStore Ref