API

• createStore(reducerObject, middleware1...middlewarenN);

2nd-level API

• dispatch(action)
• subscribe(callback(newState))
• getState()

State

A plain js object that describes the state of your application

Store

The store is nothing but a js object that gives you access to methods that mutate your app state

Reducers

Reducers are functions that accept the current slice of the state that the reducer responds to and the current action being dispatched.

Middleware

Middleware are functions that are called before an action gets to any reducers.

ReducerObject

A plain js object that is used to map keys to reducer functions. See examples below.

Normal flow --- dispatch action --- reducers --- update state

Flow with middleware --- dispatch action --- passes action through middleware(s) --- reducers --- update state

createStore

CreateStore accepts the reducer object as a first arg. And middleware functions as 2...n args

See Examples below for more details.

dispatch

This method is used to dispatch actions to the reducers which take the action and updates the state accordingly.

most actions look like this

{
    
    type : "FETCH_USER",
    extraField : "someData"
}

subscribe

This method is to be used if you would like to know when changes to the store have occurred. Ths method accepts a callback function that is invoked when the store changes.

getState

The methods returns the current state of your application

Examples

function counter(state = 0, action){
    if(action.type === 'INC'){
        return state + 1;
    } else if(action.type === 'DEC'){
        return state - 1;
    }
    return state;
}

function middlewareExample(dispatch){
    return function(getState){
        return function(action){
            console.log(action.type);
        }
    }
}
const reducerObject = { count: counter };
// normal path   dispath --- run through proper reducer
const store = createStore(reducerObject, middlewareExample);
store.dispatch({type: 'INC'});
// count is 1
function subCallack(newState){
  console.log(newState);   
}
store.subscribe(subCallback);
// everytime the store is dispatched, the newState will be given to the callback and logged

store.getState();
// {count : 1}