defaultvalue.md

Default values

defaultValue can be defined at the reducer level and the op level. If the action payload results in an undefined value for the state of that reducer, the defaultValue will be picked up if defined. For any incoming action to the reducer, if its payload extraction results in undefined, the rules of defaultValue are as follows

• If there is a defaultValue defined for the op for which the action is targeted, then that defaultValue is taken
• If there is a defaultValue defined for the reducer(outside the ops array), and there is no op level defaultValue for the op that corresponds to the incoming action, then the reducer level defaultValueis taken
• If there is neither a reducer level defaultValue nor an op level defaultValue defined for the incoming action, then the extracted payload is applied as such to the state

If transform function has been defined, the defaultValue will be passed through the transform function before applying to the state

Code

import ReducerFactory, { ops } from "@kubric/reducer-factory";
import { combineReducers, createStore } from "redux";

const factory = new ReducerFactory({
  payloadPath: "payload"
});

/**
 * Returns an object
 * {
 *   val: () => {
 *     //valReducerFunction
 *   }
 * }
 */
const reducers = reducerFactory({
  reducers: {
    val: {
      defaultState: "defaultState",
      defaultValue: "global_default_value",
      ops: [
        //assign global defaultValue to [state].val
        {
          types: [
            "GLOBAL_DEFAULTVALUE"
          ],
          op: ops.ASSIGN
        },
        //assign local defaultValue to [state].val
        {
          defaultValue: "local_default_value",
          types: [
            "LOCAL_DEFAULTVALUE"
          ],
          op: ops.ASSIGN
        },
        //assign local transformed defaultValue to [state].val
        {
          types: [
            "LOCAL_TRANSFORMED_DEFAULTVALUE"
          ],
          op: ops.ASSIGN,
          defaultValue: "local_default_value",
          transform: val => `transformed_${val}`
        },
      ]
    },
  }
});

// Create a store with the default state configured for val
const store = createStore(combineReducers(reducers));
// State:
// {
//   val: "defaultState"
// }

store.dispatch({
  type: types.GLOBAL_DEFAULTVALUE
});
// State:
// {
//   val: "global_default_value"
// }

store.dispatch({
  type: types.LOCAL_DEFAULTVALUE
});
// State:
// {
//   val: "local_default_value"
// }

store.dispatch({
  type: types.LOCAL_TRANSFORMED_DEFAULTVALUE
});
// State:
// {
//   val: "transformed_local_default_value"
// }