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You probably don't need Redux: Use React Context + useReducer hook

Nikhil Kumaran S on September 01, 2020

I would like to amend this: don't use Redux until you have problems with vanilla React. - Dan Abramov Dan said this way back in 2016, and now th...

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artydev • Sep 1 '20 • Edited

Hello, look at the Meiosis pattern.
Regards
Search Meiosis on Dev to

leob • Sep 2 '20 • Edited

First time I hear about it: dev.to/artydev/frontend-state-mana...

The explanations are terse, but yes I saw this:

meiosis.js.org/

"Think Redux, MobX, Cerebral, React Context, etc. but without having library imports everywhere and being tied to a framework API. Instead, just plain functions and objects. All you need is a simple stream library such as Flyd or Mithril Stream"

So you don't need to have library imports ... but you do need a library ;)

artydev • Sep 2 '20 • Edited

No :-)
All you need is two streams functions map and scan that you can implement yourself or use the simple implementation mithril-stream

And the function I use to merge states is a thirty lines of code called mergerino, which extends Object.assign.

I would not call them library, they are so tiny and very specialised

You can use whathever you want for the view (event document.innerHTML)

Here I use JQuery
MeiosisJS

Look at this for a starting pont :
observables

Regards

code for mergerino

const assign = Object.assign || ((a, b) => (b && Object.keys(b).forEach(k => (a[k] = b[k])), a))

const run = (isArr, copy, patch) => {
  const type = typeof patch
  if (patch && type === 'object') {
    if (Array.isArray(patch)) for (const p of patch) copy = run(isArr, copy, p)
    else {
      for (const k of Object.keys(patch)) {
        const val = patch[k]
        if (typeof val === 'function') copy[k] = val(copy[k], merge)
        else if (val === undefined) isArr && !isNaN(k) ? copy.splice(k, 1) : delete copy[k]
        else if (val === null || typeof val !== 'object' || Array.isArray(val)) copy[k] = val
        else if (typeof copy[k] === 'object') copy[k] = val === copy[k] ? val : merge(copy[k], val)
        else copy[k] = run(false, {}, val)
      }
    }
  } else if (type === 'function') copy = patch(copy, merge)
  return copy
}

const merge = (source, ...patches) => {
  const isArr = Array.isArray(source)
  return run(isArr, isArr ? source.slice() : assign({}, source), patches)
}

export default merge

the code of mithril-stream is here from Isiah Meadows Mithril's maintener.

/* eslint-disable */
;(function() {
"use strict"
/* eslint-enable */
Stream.SKIP = {}
Stream.lift = lift
Stream.scan = scan
Stream.merge = merge
Stream.combine = combine
Stream.scanMerge = scanMerge
Stream["fantasy-land/of"] = Stream

var warnedHalt = false
Object.defineProperty(Stream, "HALT", {
    get: function() {
        warnedHalt || console.log("HALT is deprecated and has been renamed to SKIP");
        warnedHalt = true
        return Stream.SKIP
    }
})

function Stream(value) {
    var dependentStreams = []
    var dependentFns = []

    function stream(v) {
        if (arguments.length && v !== Stream.SKIP) {
            value = v
            if (open(stream)) {
                stream._changing()
                stream._state = "active"
                dependentStreams.forEach(function(s, i) { s(dependentFns[i](value)) })
            }
        }

        return value
    }

    stream.constructor = Stream
    stream._state = arguments.length && value !== Stream.SKIP ? "active" : "pending"
    stream._parents = []

    stream._changing = function() {
        if (open(stream)) stream._state = "changing"
        dependentStreams.forEach(function(s) {
            s._changing()
        })
    }

    stream._map = function(fn, ignoreInitial) {
        var target = ignoreInitial ? Stream() : Stream(fn(value))
        target._parents.push(stream)
        dependentStreams.push(target)
        dependentFns.push(fn)
        return target
    }

    stream.map = function(fn) {
        return stream._map(fn, stream._state !== "active")
    }

    var end
    function createEnd() {
        end = Stream()
        end.map(function(value) {
            if (value === true) {
                stream._parents.forEach(function (p) {p._unregisterChild(stream)})
                stream._state = "ended"
                stream._parents.length = dependentStreams.length = dependentFns.length = 0
            }
            return value
        })
        return end
    }

    stream.toJSON = function() { return value != null && typeof value.toJSON === "function" ? value.toJSON() : value }

    stream["fantasy-land/map"] = stream.map
    stream["fantasy-land/ap"] = function(x) { return combine(function(s1, s2) { return s1()(s2()) }, [x, stream]) }

    stream._unregisterChild = function(child) {
        var childIndex = dependentStreams.indexOf(child)
        if (childIndex !== -1) {
            dependentStreams.splice(childIndex, 1)
            dependentFns.splice(childIndex, 1)
        }
    }

    Object.defineProperty(stream, "end", {
        get: function() { return end || createEnd() }
    })

    return stream
}

function combine(fn, streams) {
    var ready = streams.every(function(s) {
        if (s.constructor !== Stream)
            throw new Error("Ensure that each item passed to stream.combine/stream.merge/lift is a stream")
        return s._state === "active"
    })
    var stream = ready
        ? Stream(fn.apply(null, streams.concat([streams])))
        : Stream()

    var changed = []

    var mappers = streams.map(function(s) {
        return s._map(function(value) {
            changed.push(s)
            if (ready || streams.every(function(s) { return s._state !== "pending" })) {
                ready = true
                stream(fn.apply(null, streams.concat([changed])))
                changed = []
            }
            return value
        }, true)
    })

    var endStream = stream.end.map(function(value) {
        if (value === true) {
            mappers.forEach(function(mapper) { mapper.end(true) })
            endStream.end(true)
        }
        return undefined
    })

    return stream
}

function merge(streams) {
    return combine(function() { return streams.map(function(s) { return s() }) }, streams)
}

function scan(fn, acc, origin) {
    var stream = origin.map(function(v) {
        var next = fn(acc, v)
        if (next !== Stream.SKIP) acc = next
        return next
    })
    stream(acc)
    return stream
}

function scanMerge(tuples, seed) {
    var streams = tuples.map(function(tuple) { return tuple[0] })

    var stream = combine(function() {
        var changed = arguments[arguments.length - 1]
        streams.forEach(function(stream, i) {
            if (changed.indexOf(stream) > -1)
                seed = tuples[i][1](seed, stream())
        })

        return seed
    }, streams)

    stream(seed)

    return stream
}

function lift() {
    var fn = arguments[0]
    var streams = Array.prototype.slice.call(arguments, 1)
    return merge(streams).map(function(streams) {
        return fn.apply(undefined, streams)
    })
}

function open(s) {
    return s._state === "pending" || s._state === "active" || s._state === "changing"
}

if (typeof module !== "undefined") module["exports"] = Stream
else if (typeof window.m === "function" && !("stream" in window.m)) window.m.stream = Stream
else window.m = {stream : Stream}

}());

leob • Sep 2 '20

So you need to learn how think in terms of streams and observables (I think RxJS is a famous library in this area) ... if you're not familiar with that paradigm yet then it's definitely a learning curve compared to the way you'd normally do things with Redux or Context.

artydev • Sep 2 '20 • Edited

Think of streams as Excel cells and you will have a good starting point.
I have written a few lines as introduction here

streams

artydev • Sep 2 '20 • Edited

You absolutely don't need RxJS, as I said earlier you only need map and scan for Meiosis

Here is very simple stream implementaion with a map function :

function Stream (value) {
  let storedvalue = value
  let mappers = []
  function stream (newvalue) {
    if (arguments.length) {
      mappers.map(f => f(newvalue))
      storedvalue = newvalue
    }
    return storedvalue
  }
  stream.map = function (f) {
    mappers.push(f)
  }
  return stream
}

s = Stream()

document.addEventListener("mousemove", s)

s.map(t => divmouse.innerHTML = (`<h2>(${t.clientX}, ${t.clientY})</h2>`))

You can test it here :

StreamMap

Regards

leob • Sep 1 '20 • Edited

Good explanation, but I can't help but notice how similar the code looks compared to what you would write if you use Redux - you still write reducers, actions, dispatch, etcetera ... so, I could be wrong, but at first sight we don't seem to have gained much in terms of reducing boilerplate.

The only simplification then seems to be that we can omit one or two dependencies from our package.json (but Redux doesn't add that much to the bundle size, it's a pretty small library).

Note that I'm not saying that this approach (Context) is worse than using Redux, but I also don't see immediately how it's better or simpler - the way you manage state with Context is largely the same.

Or am I missing something?

Nikhil Kumaran S • Sep 1 '20

You are right. I never considered "reducing boilerplate" as a goal. I wanted to show that we can achieve redux like functionality in vanilla react itself.

leob • Sep 2 '20

Understood ... but look at this one - we might not need Redux, but we might even also not need Context! dev.to/g_abud/why-i-quit-redux-1knl

Nikhil Kumaran S • Sep 2 '20

Sure will check it out✌🏽

Sylvester • Sep 1 '20

Really nice introduction to Context. Is there a well-established way to use asynchronous actions, similar to redux thunk?

Nikhil Kumaran S • Sep 1 '20

You can declare an async function in the value prop to the Provider. Here's an example: codesandbox

P.S. Not sure if this exactly what you asked for.

Sylvester • Sep 1 '20

Yes, this is it. It occurred to me when I saw the example that I don't need middleware to access state - here I can simply refer to it if I need for example some intersection between fetched data and current state.

Thank you :-)

Nikhil Kumaran S • Sep 1 '20

You're welcome👍🏽

leo 👨🏻‍💻 • Sep 1 '20

It was! Thanks mate :)

Nikhil Kumaran S • Sep 1 '20 • Edited

Glad you liked it.