在一个简单的RxJS示例中，如何在不使用主题或命令式操纵的情况下管理状态? [英] How to manage state without using Subject or imperative manipulation in a simple RxJS example?

问题描述

我已经在RxJS上进行了两个星期的实验，尽管我原则上喜欢RxJS，但是我似乎无法找到并实现用于管理状态的正确模式.所有文章和问题似乎都同意:

I have been experimenting with RxJS for two weeks now, and although I love it in principle I just cannot seem to find and implement the correct pattern for managing state. All articles and questions appear to agree:

应尽可能避免使用
• Subject ，而只是通过转换来推动状态； <​​/li>
• .getValue()应该完全不推荐使用；和
除了DOM操作外，也许应该避免
• .do 吗?

• Subject should be avoided where possible in favor of just pushing state through via transformations;
• .getValue() should be deprecated entirely; and
• .do should perhaps be avoided except for DOM manipulation?

所有此类建议的问题在于，除了您将学习Rx方式并停止使用Subject"之外，没有文献似乎直接说出您应该使用的内容.

The problem with all such suggestions is that none of the literature appears to directly say what you should be using instead, besides "you'll learn the Rx way and stop using Subject".

但是我无法在任何地方找到直接的示例，该示例明确指出了以无状态和功能性方式对单个流/对象执行添加和移除的正确方法，这是多个其他流输入的结果.

But I cannot find a direct example anywhere that specifically indicates the correct way to perform both additions and removals to a single stream/object, as the consequence of multiple other stream inputs, in a stateless and functional manner.

在我再次指出相同的方向之前，未发现的文献存在的问题是:

Before I get pointed in the same directions again, problems with uncovered literature are:

• 反应式编程简介您一直缺少:很好的开始文本，但没有具体解决这些问题.
• RxJS的TODO示例随React一起提供，涉及显式操纵 Subject 作为React Store的代理.
• http://blog.edanschwartz.com/2015/09/18/dead-simple-rxjs-todo-list/:显式使用 state 对象添加和删除项目.

• The Introduction to Reactive Programming You've been missing: great starting text, but does not specifically address these questions.
• The TODO example for RxJS comes with React and involves explicit manipulation of Subjects as proxies for React Stores.
• http://blog.edanschwartz.com/2015/09/18/dead-simple-rxjs-todo-list/ : explicitly uses a state object for addition and removal of items.

下面是我对标准TODO的第10次重写-我之前涉及的迭代包括:

My perhaps 10th rewrite of the standard TODO follows - My prior iterations covered include:

• 从可变的"items"数组开始-糟糕，因为状态是显式的且必须进行管理
• 使用 scan 将新项目连接到 addedItems $ 流中，然后在另一个流中删除已删除项目的分支-糟糕的是 addedItems $ 流将无限期增长.
• 发现 BehaviorSubject 并使用它-似乎很糟糕，因为对于每个新的 updatedList $ .next()发射，它都需要迭代先前的值，这意味着Subject.getValue()是必不可少的.
• 尝试将 inputEnter $ 添加事件的结果流式传输到过滤的删除事件中-但是随后每个新流都创建一个新列表，然后将其馈送到 toggleItem $ 和 toggleAll $ 流意味着每个新流都依赖于前一个流，因此导致4个操作之一(添加，删除，切换项目或全部切换)需要整个链不必要地运行再次通过.

• starting with a mutable 'items' array - bad as state is explicit and imperatively managed
• using scan to concatenate new items to an addedItems$ stream, then branching another stream where the removed items were deleted - bad as the addedItems$ stream would grow indefinitely.
• discovering BehaviorSubjectand using that - seemed bad since for each new updatedList$.next() emission, it requires the previous value to iterate, meaning that Subject.getValue() is essential.
• trying to stream the result of the inputEnter$ addition events into filtered removal events - but then every new stream creates a new list, and then feeding that into the toggleItem$ and toggleAll$ streams means that each new stream is dependent on the previous, and so causing one of the 4 actions (add, remove, toggle item or toggle all) requires the whole chain to be unnecessarily run through again.

现在，我已经转了整整一个圈，回到了同时使用 Subject (以及不使用 getValue()的情况下应该如何对其进行连续迭代的方式)

Now I have come full circle, where I am back to using both Subject (and just how is it supposed to be successively iterated upon in any way without using getValue()?) and do, as show below. Myself and my colleague agree this is the clearest way, yet it of course seems the least reactive and most imperative. Any clear suggestions on the correct way for this would be much appreciated!

import Rx from 'rxjs/Rx';
import h from 'virtual-dom/h';
import diff from 'virtual-dom/diff';
import patch from 'virtual-dom/patch';

const todoListContainer = document.querySelector('#todo-items-container');
const newTodoInput = document.querySelector('#new-todo');
const todoMain = document.querySelector('#main');
const todoFooter = document.querySelector('#footer');
const inputToggleAll = document.querySelector('#toggle-all');
const ENTER_KEY = 13;

// INTENTS
const inputEnter$ = Rx.Observable.fromEvent(newTodoInput, 'keyup')
    .filter(event => event.keyCode === ENTER_KEY)
    .map(event => event.target.value)
    .filter(value => value.trim().length)
    .map(value => {
        return { label: value, completed: false };
    });

const inputItemClick$ = Rx.Observable.fromEvent(todoListContainer, 'click');

const inputToggleAll$ = Rx.Observable.fromEvent(inputToggleAll, 'click')
    .map(event => event.target.checked);

const inputToggleItem$ = inputItemClick$
    .filter(event => event.target.classList.contains('toggle'))
    .map((event) => {
        return {
            label: event.target.nextElementSibling.innerText.trim(),
            completed: event.target.checked,
        };
    })

const inputDoubleClick$ = Rx.Observable.fromEvent(todoListContainer, 'dblclick')
    .filter(event => event.target.tagName === 'LABEL')
    .do((event) => {
        event.target.parentElement.classList.toggle('editing');
    })
    .map(event => event.target.innerText.trim());

const inputClickDelete$ = inputItemClick$
    .filter(event => event.target.classList.contains('destroy'))
    .map((event) => {
        return { label: event.target.previousElementSibling.innerText.trim(), completed: false };
    });

const list$ = new Rx.BehaviorSubject([]);

// MODEL / OPERATIONS
const addItem$ = inputEnter$
    .do((item) => {
        inputToggleAll.checked = false;
        list$.next(list$.getValue().concat(item));
    });

const removeItem$ = inputClickDelete$
    .do((removeItem) => {
        list$.next(list$.getValue().filter(item => item.label !== removeItem.label));
    });

const toggleAll$ = inputToggleAll$
    .do((allComplete) => {
        list$.next(toggleAllComplete(list$.getValue(), allComplete));
    });

function toggleAllComplete(arr, allComplete) {
    inputToggleAll.checked = allComplete;
    return arr.map((item) =>
        ({ label: item.label, completed: allComplete }));
}

const toggleItem$ = inputToggleItem$
    .do((toggleItem) => {
        let allComplete = toggleItem.completed;
        let noneComplete = !toggleItem.completed;
        const list = list$.getValue().map(item => {
            if (item.label === toggleItem.label) {
                item.completed = toggleItem.completed;
            }
            if (allComplete && !item.completed) {
                allComplete = false;
            }
            if (noneComplete && item.completed) {
                noneComplete = false;
            }
            return item;
        });
        if (allComplete) {
            list$.next(toggleAllComplete(list, true));
            return;
        }
        if (noneComplete) {
            list$.next(toggleAllComplete(list, false));
            return;
        }
        list$.next(list);
    });

// subscribe to all the events that cause the proxy list$ subject array to be updated
Rx.Observable.merge(addItem$, removeItem$, toggleAll$, toggleItem$).subscribe();

list$.subscribe((list) => {
    // DOM side-effects based on list size
    todoFooter.style.visibility = todoMain.style.visibility =
        (list.length) ? 'visible' : 'hidden';
    newTodoInput.value = '';
});

// RENDERING
const tree$ = list$
    .map(newList => renderList(newList));

const patches$ = tree$
    .bufferCount(2, 1)
    .map(([oldTree, newTree]) => diff(oldTree, newTree));

const todoList$ = patches$.startWith(document.querySelector('#todo-list'))
    .scan((rootNode, patches) => patch(rootNode, patches));

todoList$.subscribe();


function renderList(arr, allComplete) {
    return h('ul#todo-list', arr.map(val =>
        h('li', {
            className: (val.completed) ? 'completed' : null,
        }, [h('input', {
                className: 'toggle',
                type: 'checkbox',
                checked: val.completed,
            }), h('label', val.label),
            h('button', { className: 'destroy' }),
        ])));
}

编辑

关于@ user3743222非常有用的答案，我可以看到将状态表示为附加输入如何使函数纯净，因此 scan 是表示随时间演变的集合的最佳方法，到该点为止的先前状态的快照作为附加功能参数.

Edit

In relation to @user3743222 very helpful answer, I can see how representing state as an additional input can make a function pure and thus scan is the best way to represent a collection evolving over time, with a snapshot of its previous state up to that point as an additional function parameter.

但是，这已经是我进行第二次尝试的方式了， addedItems $ 是输入的扫描流:

However, this was already how I approached my second attempt, with addedItems$ being a scanned stream of inputs:

// this list will now grow infinitely, because nothing is ever removed from it at the same time as concatenation?
const listWithItemsAdded$ = inputEnter$
    .startWith([])
    .scan((list, addItem) => list.concat(addItem));

const listWithItemsAddedAndRemoved$ = inputClickDelete$.withLatestFrom(listWithItemsAdded$)
    .scan((list, removeItem) => list.filter(item => item !== removeItem));

// Now I have to always work from the previous list, to get the incorporated amendments...
const listWithItemsAddedAndRemovedAndToggled$ = inputToggleItem$.withLatestFrom(listWithItemsAddedAndRemoved$)
    .map((item, list) => {
        if (item.checked === true) {
        //etc
        }
    })
    // ... and have the event triggering a bunch of previous inputs it may have nothing to do with.


// and so if I have 400 inputs it appears at this stage to still run all the previous functions every time -any- input
// changes, even if I just want to change one small part of state
const n$ = nminus1$.scan...

显而易见的解决方案是只具有 items = [] ，然后直接对其进行操作，或者 const items = new BehaviorSubject([])-但只有一个进行迭代的方法似乎是使用 getValue 公开以前的状态，Andre Stalz(CycleJS)在RxJS问题中对此进行了评论，认为它实际上不应公开(但是如果否，那么它怎么用?).

The obvious solution would be to just have items = [], and manipulate it directly, or const items = new BehaviorSubject([]) - but then the only way to iterate on it appears to be using getValue to expose the previous state, which Andre Stalz (CycleJS) has commented on in the RxJS issues as something that shouldn't really be exposed (but again, if not, then how is it usable?).

我想我只是有一个想法，对于流，您不应该使用主题"或通过肉丸"状态表示任何内容，并且在第一个答案中，我不确定这不会引入质量链孤立的/无限增长的/必须相互依序建立的流.

I guess I just had an idea that with streams, you weren't supposed to use Subjects or represent anything via a state 'meatball', and in the first answer I'm not sure how this doesn't introduce mass chained streams which are orphaned/grow infinitely/have to build on each other in exact sequence.

推荐答案

我认为您已经找到了一个很好的示例: http://jsbin.com/redeko/edit?js，输出.

I think you already found a good example with : http://jsbin.com/redeko/edit?js,output.

您对此实施的事实持怀疑态度

You take issue with the fact that this implementation

明确地使用状态对象来添加和删除项目.

explicitly uses a state object for addition and removal of items.

但是，thas正是您要寻找的良好实践.例如，如果重命名该状态对象 viewModel ，则对您来说可能更明显.

However, thas is exactly the good practice you are looking for. If you rename that state object viewModel for example, it might be more apparent to you.

会有其他定义，但是我想将状态定义如下:

There will be other definitions but I like to think of state as follows:

• 给了 f 一个不纯函数，即 output = f(input)，这样您就可以为同一个输入拥有不同的输出，即与该函数相关联的状态((如果存在)是额外的变量，使得 f(input)= output = g(input，state)成立，而g是纯函数.

• given f an impure function, i.e. output = f(input), such that you can have different outputs for the same input, the state associated to that function (when it exists) is the extra variable such that f(input) = output = g(input, state) holds and g is a pure function.

因此，如果此处的功能是将代表用户输入的对象与todo数组匹配，并且如果我在已经有2个todo的todo列表上单击 add ，则输出将为3个待办事项.如果我只用一个待办事项在待办事项列表上执行相同(相同的输入)，则输出将是2个待办事项.因此，相同的输入，不同的输出.

So if the function here is to match an object representing a user input, to an array of todo, and if I click add on a todo list with already have 2 todos, the output will be 3 todos. If I do the same (same input) on a todo list with only one todo, the output will be 2 todos. So same input, different outputs.

此处允许将该函数转换为纯函数的状态是todo数组的当前值.因此，我的输入变成了 add 点击， AND ，并通过函数 g 传递了当前的待办事项数组，该函数提供了一个具有新todo的新todo数组列表.该函数g是纯函数.因此，通过在 g 中明确显示以前隐藏的状态，可以以无状态方式实现 f .

The state here that allows to transform that function into a pure function is the current value of the todo array. So my input becomes an add click, AND the current todo array, passed through a function g which give a new todo array with a new todo list. That function g is pure. So f is implemented in a stateless way by making its previously hidden state explicit in g.

这非常适合围绕纯函数编写的函数式编程.

And that fits well with functional programming which revolves around composing pure functions.

• 扫描

因此，在使用RxJS或其他方法进行状态管理时，一个好的做法是使状态显式进行操作.

So when it comes to state management, with RxJS or else, a good practice is to make state explicit to manipulate it.

如果将 output = g(input，state)转换为流，则会得到 On + 1 = g(In + 1，Sn)，这就是 scan 运算符的作用.

If you turn the output = g(input, state) into a stream, you get On+1 = g(In+1, Sn) and that's exactly what the scan operator does.

• 展开

另一个概括了 scan 的运算符是 expand ，但是到目前为止，我很少使用该运算符. scan 通常可以解决问题.

Another operator which generalizes scan is expand, but so far I had very little use of that operator. scan generally does the trick.

很抱歉，答案冗长而含糊.我花了一些时间来解决这些概念，这就是我使它们对我可以理解的方式.希望它也对您有用.

Sorry for the long and mathy answer. It took me a while to get around those concepts and that's the way I made them understandable for me. Hopefully it works for you too.

这篇关于在一个简单的RxJS示例中，如何在不使用主题或命令式操纵的情况下管理状态?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！