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Redux without the sanity checks in a single file. Don't use this, use normal Redux. :-)
function mapValues(obj, fn) {
return Object.keys(obj).reduce((result, key) => {
result[key] = fn(obj[key], key);
return result;
}, {});
}
function pick(obj, fn) {
return Object.keys(obj).reduce((result, key) => {
if (fn(obj[key])) {
result[key] = obj[key];
}
return result;
}, {});
}
function bindActionCreator(actionCreator, dispatch) {
return (...args) => dispatch(actionCreator(...args));
}
export function bindActionCreators(actionCreators, dispatch) {
return typeof actionCreators === 'function' ?
bindActionCreator(actionCreators, dispatch) :
mapValues(actionCreators, actionCreator =>
bindActionCreator(actionCreator, dispatch)
);
}
export function compose(...funcs) {
return arg => funcs.reduceRight((composed, f) => f(composed), arg);
}
export function applyMiddleware(...middlewares) {
return (next) => (reducer, initialState) => {
var store = next(reducer, initialState);
var dispatch = store.dispatch;
var chain = [];
chain = middlewares.map(middleware => middleware({
getState: store.getState,
dispatch: (action) => dispatch(action)
}));
dispatch = compose(...chain)(store.dispatch);
return { ...store, dispatch };
};
}
export function combineReducers(reducers) {
var finalReducers = pick(reducers, (val) => typeof val === 'function');
return (state = {}, action) => mapValues(finalReducers,
(reducer, key) => reducer(state[key], action)
);
}
export function createStore(reducer, initialState) {
var currentReducer = reducer;
var currentState = initialState;
var listeners = [];
var isDispatching = false;
function getState() {
return currentState;
}
function subscribe(listener) {
listeners.push(listener);
return function unsubscribe() {
var index = listeners.indexOf(listener);
listeners.splice(index, 1);
};
}
function dispatch(action) {
if (isDispatching) {
throw new Error('Reducers may not dispatch actions.');
}
try {
isDispatching = true;
currentState = currentReducer(currentState, action);
} finally {
isDispatching = false;
}
listeners.slice().forEach(listener => listener());
return action;
}
function replaceReducer(nextReducer) {
currentReducer = nextReducer;
dispatch({ type: '@@redux/INIT' });
}
dispatch({ type: '@@redux/INIT' });
return { dispatch, subscribe, getState, replaceReducer };
}

Genius is not measured in LOC.

Brilliant

omnidan commented Sep 26, 2015

I was mind-blown when someone asked me how redux-thunk worked and I checked the code only to realize it has 6 lines in total. This blew my mind even more 😅

snehesht commented Oct 5, 2015

Awesome.

dbrans commented Oct 13, 2015

@gaearon, In the current revision, in applyMiddleware, the initial value of var dispatch = store.dispatch is never used. Did you meant to use it on line 43?
https://gist.github.com/gaearon/ffd88b0e4f00b22c3159/4c9a62c6a2b353842dd2b6d15b9ca363ad4161e3#file-slim-redux-js-L36

I love this :-) I think redux has the highest GitHub stars per line of code of all time. 80 stars per line ;-)

dlwalsh commented Oct 27, 2015

Is there a reason why mapValues (and also pick) looks like this:

function mapValues(obj, fn) {
  return Object.keys(obj).reduce((result, key) => {
    result[key] = fn(obj[key], key);
    return result;
  }, {});
}

and not the more idiomatic:

function mapValues(obj, fn) {
  return Object.keys(obj).reduce((result, key) => (
    Object.assign({}, result, {
      [key]: fn(obj[key], key);
    });
  ), {});
}

Is it a case of performance over purity?

@dlwalsh or for that matter:

function mapValues(obj, fn) {
  return Object.keys(obj).reduce((result, key) => ({
    ...result,
    [key]: fn(obj[key], key)
  }), {});
}

acusti commented Dec 1, 2015

@dbrans The initial dispatch function in applyMiddleware is used on line 41 within the body of the wrapped dispatch (i.e. next) function passed to each middleware.

@dlwalsh, result is created inside the mapValues function and passed to reduce as initial value (also called an accumulator). Because it’s created inside mapValues, it can be mutated and mapValues would still be a pure function.

dtinth commented May 4, 2016

@dlwalsh It’s algorithmic complexity. The “purer” version is O(n2) where the original version is O(n), so it’s not the same as using for loops vs Array#reduce. Here’s a benchmark:

function mapValues1(obj, fn) {
  return Object.keys(obj).reduce((result, key) => {
    result[key] = fn(obj[key], key);
    return result;
  }, {});
}

function mapValues2(obj, fn) {
  return Object.keys(obj).reduce((result, key) => (
    Object.assign({}, result, {
      [key]: fn(obj[key], key)
    })
  ), {});
}

var obj = { }
for (var i = 0; i < 10000; i ++) obj[i] = i

var mapper = x => x * x

console.time('mapValues1')
var result1 = mapValues1(obj, mapper)
console.timeEnd('mapValues1')

console.time('mapValues2')
var result2 = mapValues2(obj, mapper)
console.timeEnd('mapValues2')

// Ensure result is correct :)
require('assert').equal(result1[100], 10000)
require('assert').deepEqual(result1, result2)

Result:

mapValues1: 7.764ms
mapValues2: 10896.908ms

You can see that it takes 10 seconds to map a 10000-key object if you create a new object every time. Both functions are equally pure as @CrocoDillon said, since all the mutations happen inside the function.

davesnx commented May 4, 2016

Well tested @dtinth, but it's basically the Object.assign creates a new object(with result and matches the key) each iteration, and the mapValues1 just add as a key in the resultant object.

Pure Genius!

I did the same for my Redux Course to explain how really Redux works and what is the concept. I notice that in a lot of courses about Redux, teachers miss the importance of selectors...

Artistic

It's possible to slim it down even further by removing the isDispatching checks! Then it would be < 90 lines!

sabha commented Oct 24, 2016

Thanks Dan. Do we have similar one for React-Redux. Trying to understand the connect method for adding features like "Resolve data before mounting the container".

jakl commented Dec 13, 2016

I would love to watch a youtube video going over in detail every line of this code.

Awesome. Simple but not simpler 👍

ehzawad commented Feb 24, 2017

Cool

Haters don't hate you know it's genius... #imnotworthy#

ptim commented Jun 11, 2017

@sabha you probably found it already, but for those who com after, here is connect explained: https://gist.github.com/gaearon/1d19088790e70ac32ea636c025ba424e

Amazingly beautiful code 👍

I'm heavily breathing right now. This is just pure awesomeness!

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