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輕鬆應付複雜的⾮非同步操作 RxJS + Redux Observable Huli

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胡⽴立 Hu Li • 東南亞新創公司 Eatigo Frontend Team Lead • TechBridge Weekly 技術週刊編輯 
 致⼒力於淺顯易懂的程式教學，搞不好你看過我的⽂文章 • [⼼心得] ⼗十年程式⾃自學之路 • 零基礎的⼩小明要如何成為前端⼯工程師？ • 跟著⼩小明⼀一起搞懂技術名詞：MVC、SPA 與 SSR • 資料庫的好夥伴：Redis • 讓我們來談談 CSRF • 希望是最淺顯易懂的 RxJS 教學 aszx87410@gmail.com

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開始之前 4⽉月底 RxJS 5 => RxJS 6
 6⽉月底 redux-observable v0.x => v1.0.0 由於概念不變，簡報中舉的例⼦子都是
 RxJS5 + redux-observable v0.x

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什麼是 ReactiveX?

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與其讓我告訴你那是什麼 不如你⾃自⼰己體會

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⼩小試⾝身⼿手 現在有⼀一個陣列，裡⾯面每個元素都是⾃自然數
 請你把奇數挑出來，並且平⽅方之後加總

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const solution = arr => {
 let ans = 0
 for(let i=0; i

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有沒有其他解法？

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const solution = arr => {
 return arr
 .filter(val => val % 2)
 .map(val => val * val)
 .reduce(
 (total, val) => total + val
 )
 }

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const solution = arr => {
 let ans = 0
 for(let i=0; i {
 return arr
 .filter(val => val % 2)
 .map(val => val * val)
 .reduce(
 (total, val) => total + val
 )
 }

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const solution = arr => {
 let ans = 0
 for(let i=0; i {
 return arr
 .filter(val => val % 2)
 .map(val => val * val)
 .reduce(
 (total, val) => total + val
 )
 } Imperative 命令式 什麼東⻄西都⾃自⼰己來，⼼心 hen 累

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const solution = arr => {
 let ans = 0
 for(let i=0; i {
 return arr
 .filter(val => val % 2)
 .map(val => val * val)
 .reduce(
 (total, val) => total + val
 )
 } Imperative 命令式 什麼東⻄西都⾃自⼰己來，⼼心 hen 累 Declarative 聲明式 告訴電腦：我想要什麼

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⼩小試⾝身⼿手 現在有兩堆資料 orders 跟 members
 請找出⾦金額 > 100 且 id > 10 的資料
 並且加上會員資料⼀一併回傳

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const solution = (orders, members) => {
 const ans = []
 for(let i=0; i 100 && orders[i].id > 10) {
 ans.push({
 order: orders[i],
 member: members[orders.memberId]
 })
 }
 }
 return ans
 } Imperative 命令式 什麼東⻄西都⾃自⼰己來，⼼心 hen 累

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const solution = (orders, members) => {
 const ans = []
 for(let i=0; i 100 && orders[i].id > 10) {
 ans.push({
 order: orders[i],
 member: members[orders.memberId]
 })
 }
 }
 return ans
 } const solution = (orders, members) => {
 return orders
 .filter(o => o.amount > 100)
 .filter(o => o.id > 10)
 .map(o => ({
 order: o,
 member: members[o.memberId] 
 }))
 } Imperative 命令式 什麼東⻄西都⾃自⼰己來，⼼心 hen 累 Declarative 聲明式 告訴電腦：我想要什麼

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其實你早就學過 Declarative

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const solution = (orders, members) => {
 const ans = []
 for(let i=0; i 100 && orders[i].id > 10) {
 ans.push({
 order: orders[i],
 member: members[orders.memberId]
 })
 }
 }
 return ans
 } SELECT * FROM orders
 WHERE orders.amount > 100 AND orders.id > 10
 JOIN members ON members.id = orders.memberId Imperative 命令式 什麼東⻄西都⾃自⼰己來，⼼心 hen 累 Declarative 聲明式 告訴電腦：我想要什麼

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把資料經過⼀一連串轉換
 得出想要的結果

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1 2 3 4 5 6

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1 2 3 4 5 6 filter (取奇數)

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1 2 3 4 5 6 filter (取奇數) 1 3 5

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1 2 3 4 5 6 filter (取奇數) 1 3 5 map (平⽅方)

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1 2 3 4 5 6 filter (取奇數) 1 3 5 map (平⽅方) 1 9 25

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1 2 3 4 5 6 filter (取奇數) 1 3 5 map (平⽅方) 1 9 25 reduce (加總)

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1 2 3 4 5 6 filter (取奇數) 1 3 5 map (平⽅方) 1 9 25 reduce (加總) 35

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重點⼀一
 
 把資料經過⼀一連串轉換
 得出想要的結果

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Reactive
 反應、反應性的

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window.addEventListener(
 'click',() => { console.log('click!') }
 )

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重點⼆二
 當某事發⽣生，我能做出反應

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1. 某事發⽣生，我能做出反應
 2. 把資料經過轉換得出答案

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Rx.Observable.fromEvent(window, 'click')
 .map(e => e.target)
 .subscribe(value => { console.log(‘click!’, value) }
 )

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Rx.Observable.fromEvent(window, 'click')
 .map(e => e.target)
 .subscribe(value => { console.log(‘click!’, value) }
 ) 當某事發⽣生，我能做出反應

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Rx.Observable.fromEvent(window, 'click')
 .map(e => e.target)
 .subscribe(value => { console.log(‘click!’, value) }
 ) 把資料經過轉換

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Rx.Observable.fromEvent(window, 'click')
 .map(e => e.target)
 .subscribe(value => { console.log(‘click!’, value) }
 ) 得出我想要的答案

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Rx.Observable.fromEvent(window, 'click')
 .map(e => e.target)
 .subscribe(value => { console.log(‘click!’, value) }
 )

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Observable 可被觀察的
 
 可以想成 stream 資料流
 會隨著時間增加元素的陣列

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Rx.Observable.fromEvent(window, 'click')
 .map(e => 1)
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 )

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click map scan (加總)

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click map scan (加總) 1

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click map scan (加總) 1 1

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click click map scan (加總) 1 1

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click click map scan (加總) 1 1 1

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click click map scan (加總) 1 1 1 2

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click click click map scan (加總) 1 1 1 2

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click click click map scan (加總) 1 1 1 1 2

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click click click map scan (加總) 1 1 1 1 2 3

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RxJS 的威⼒力所在：組合技


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兩個陣列合併會變什麼？

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[1, 2, 3] 跟 [4, 5, 6]
 
 串接：[1, 2, 3, 4, 5, 6]
 相加：[5, 7, 9]

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兩個 Observable 合併會變什麼？

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兩個 Observable 合併會變什麼？ 會隨著時間增加元素的陣列

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10 40 7 30 5 merge 10 40 7 30 5

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可以把兩個資料流合併！

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) +1 -1

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) merge +1 -1

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) +1 merge +1 -1

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) +1 merge +1 +1 -1

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) +1 +1 merge +1 +1 -1

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) +1 +1 merge +1 +1 +1 -1

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) +1 +1 -1 merge +1 +1 +1 -1

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) +1 +1 -1 merge +1 +1 -1 +1 -1

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) +1 +1 +1 -1 merge +1 +1 -1 +1 -1

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) +1 +1 +1 -1 merge +1 +1 +1 -1 +1 -1

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) +1 +1 +1 -1 -1 merge +1 +1 +1 -1 +1 -1

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) +1 +1 +1 -1 -1 merge +1 +1 +1 -1 -1 +1 -1

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Rx.Observable.fromEvent(plus, 'click')
 .mapTo(1)
 .merge(
 Rx.Observable.fromEvent(minus, 'click')
 .mapTo(-1)
 )
 .scan((total, val) => total + val)
 .subscribe(value => { console.log(‘click!’, value) }
 ) var total = 0 plus.addEventListener('click', () => {
 total++
 console.log(‘click!’, total)
 })
 
 minus.addEventListener('click', () => {
 total—
 console.log(‘click!’, total)
 })

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RxJS 與 Promise

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當某事發⽣生，我能做出反應

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當某事發⽣生，我能做出反應 當 Promise 完成時

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function getData() {
 return fetch('http://example.com/api')
 .then(res => res.json()) 
 }
 
 Rx.Observable.fromPromise(getData())
 .subscribe(response => { console.log(response) }
 )

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Rx.Observable.fromEvent(window, 'click')
 .map(e =>
 Rx.Observable.fromPromise(getData())
 )
 .subscribe(response => { console.log(response) })

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Rx.Observable.fromEvent(window, 'click')
 .map(e =>
 Rx.Observable.fromPromise(getData())
 )
 .subscribe(response => { console.log(response) })

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click Rx.Observable.fromEvent(window, 'click')
 .map(e =>
 Rx.Observable.fromPromise(getData())
 )
 .subscribe(response => { console.log(response) })

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click Rx.Observable.fromEvent(window, 'click')
 .map(e =>
 Rx.Observable.fromPromise(getData())
 )
 .subscribe(response => { console.log(response) }) click Observable response

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[[1, 2], [3, 4, 5], [6], 7]
 想把陣列壓平怎麼辦？

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_.flatten(arr)

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click Rx.Observable.fromEvent(window, 'click')
 .map(e =>
 Rx.Observable.fromPromise(getData())
 )
 .subscribe(response => { console.log(response) }) click Observable response

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click Rx.Observable.fromEvent(window, 'click')
 .flatMap(e =>
 Rx.Observable.fromPromise(getData())
 )
 .subscribe(response => { console.log(response) }) click response

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click Rx.Observable.fromEvent(window, 'click')
 .flatMap(e =>
 Rx.Observable.fromPromise(getData())
 )
 .subscribe(response => { console.log(response) }) click response click

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click Rx.Observable.fromEvent(window, 'click')
 .flatMap(e =>
 Rx.Observable.fromPromise(getData())
 )
 .subscribe(response => { console.log(response) }) click response click response

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mergeMap(flatMap)
 concatMap
 switchMap

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mergeMap 很簡單，就是 parallel

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mergeMap 很簡單，就是 parallel click request

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mergeMap 很簡單，就是 parallel click request request

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mergeMap 很簡單，就是 parallel click request request request

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mergeMap 很簡單，就是 parallel click request response request request

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mergeMap 很簡單，就是 parallel click request response request request response

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mergeMap 很簡單，就是 parallel click request response request response request response

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mergeMap 很簡單，就是 parallel
 response 順序不代表 request 的順序 click request response request response request response

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mergeMap 可以限制 concurrency 數量
 假設設定為 1

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mergeMap 可以限制 concurrency 數量
 假設設定為 1 click request

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mergeMap 可以限制 concurrency 數量
 假設設定為 1 click request response

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mergeMap 可以限制 concurrency 數量
 假設設定為 1 click request response request

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mergeMap 可以限制 concurrency 數量
 假設設定為 1 click request response request response

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mergeMap 可以限制 concurrency 數量
 假設設定為 1 click request response request response request

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mergeMap 可以限制 concurrency 數量
 假設設定為 1 click request response response request response request

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concatMap 執⾏行完⼀一個才會執⾏行下⼀一個
 就是 mergeMap(… , 1) click request response response request response request

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switchMap 只取最後⼀一個 request 的 response
 是很常⽤用的⼀一個⽅方法 click request response response request response request

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No content

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A 餐廳

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A 餐廳 回上⼀一⾴頁

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A 餐廳 回上⼀一⾴頁 B 餐廳

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⾮非同步的問題 假設 A 的 response 花了 3 秒
 B 的 response 只花了 1 秒

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⾮非同步的問題 假設 A 的 response 花了 3 秒
 B 的 response 只花了 1 秒 mergeMap：1 秒後顯⽰示 B，3 秒後顯⽰示 A

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⾮非同步的問題 假設 A 的 response 花了 3 秒
 B 的 response 只花了 1 秒 mergeMap：1 秒後顯⽰示 B，3 秒後顯⽰示 A
 concatMap：3 秒後顯⽰示 A，4 秒後顯⽰示 B


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⾮非同步的問題 假設 A 的 response 花了 3 秒
 B 的 response 只花了 1 秒 mergeMap：1 秒後顯⽰示 B，3 秒後顯⽰示 A
 concatMap：3 秒後顯⽰示 A，4 秒後顯⽰示 B
 switchMap：1 秒後顯⽰示 B

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⾮非同步的問題 假設 A 的 response 花了 3 秒
 B 的 response 只花了 1 秒 mergeMap：1 秒後顯⽰示 B，3 秒後顯⽰示 A
 concatMap：3 秒後顯⽰示 A，4 秒後顯⽰示 B
 switchMap：1 秒後顯⽰示 B 很常⽤用的原因：只要管最新的 request

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Redux 與 RxJS

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核⼼心概念：action in, action out
 在 middleware ⽤用 RxJS 解決⼀一切 redux-observable Action
 getUser middleware epic Action
 setUser API Server

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redux-observable

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const getUserEpic = action$ => action$.ofType(actionTypes.GET_USER)
 .switchMap(action => 
 Rx.Observable.fromPromise(API.getUser(
 action.payload.id
 ))
 .map(user => setUser(user))
 .catch(err => Observable.of(getUserError(err)))
 )
 Epic

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const getUserEpic = action$ => action$.ofType(actionTypes.GET_USER)
 .switchMap(action => 
 Rx.Observable.fromPromise(API.getUser(
 action.payload.id
 ))
 .map(user => setUser(user))
 .catch(err => Observable.of(getUserError(err)))
 )
 Action in, Action out

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與其他 Middleware 的⽐比較

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dispatch ⼀一個 promise，middleware 幫你執⾏行 redux-promise const getUser = id => ({
 type:'GET_USER',
 payload:API.getUser(id)
 }) middleware redux-promise GET_USER_PENDING
 GET_USER_FULFILLED
 GET_USER_REJECTED API Server

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dispatch ⼀一個 function，middleware 幫你執⾏行 redux-thunk const getUser = id => { return dispatch => { return API.getUser(id).then( user => dispatch(setUser(user)) ).catch( err => dispatch(getUserError(err)) ) } }

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與 redux-observable 類似，都是 dispatch pure action
 其餘的讓 saga 去處理 redux-saga Action
 getUser middleware saga Action
 setUser API Server

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監聽指定的 action，並且丟給 worker 處理 watcher function* watcherSaga() { yield takeLatest("GET_USER", fetchUser) } takeLatest：只拿最後⼀一個（switchMap）
 takeEvery：每個都拿（mergeMap）

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call API 並且 dispatch 結果 worker function* fetchUser(action) { try { const user = yield call(
 API.getUser, action.payload.id
 ) yield put(setUser(user)) } catch (err) { yield put(getUserError(err)) } }

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簡單⽐比較 promise thunk saga observable 學習難度 ☆ ☆☆ ☆☆☆☆☆ ☆☆☆☆☆ Action 型態 Promise Function Object Object ⾮非同步
 流程管理 X X O O ⽅方便測試 X X O O

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RxJS 與各種複雜情境

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情境⼀一：巢狀 API /api/posts/:id
 /api/posts/:id/translations

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情境⼀一：巢狀 API /api/posts/:id
 /api/posts/:id/translations const epic = action$ => action$.ofType(actionTypes.GET_POST)
 .switchMap(action =>
 Observable.forkJoin( Observable.from(API.getPost(id)),
 Observable.from(API.getTrans(id))
 )
 .map(data => Actions.setPost({
 post: data[0],
 translations: data[1]
 })
 )
 )

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情境⼀一：巢狀 API /api/posts/:id
 /api/posts/:id/translations const epic = action$ => action$.ofType(actionTypes.GET_POST)
 .switchMap(action =>
 Observable.forkJoin( Observable.from(API.getPost(id)),
 Observable.from(API.getTrans(id))
 )
 .map(data => Actions.setPost({
 post: data[0],
 translations: data[1]
 })
 )
 )

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情境⼆二：call 兩個 API /api/posts/:id
 /api/users/:id

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情境⼆二：call 兩個 API /api/posts/:id
 /api/users/:id action$.ofType(GET_POST).switchMap(action => Observable.from(API.getPost(action.id))
 .mergeMap(post => Observable.from(API.getUser(post.authorId))
 .map(user => Actions.setPost({
 post,
 user
 })
 )
 ) 
 )

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情境⼆二：call 兩個 API /api/posts/:id
 /api/users/:id action$.ofType(GET_POST).switchMap(action => Observable.from(API.getPost(action.id))
 .mergeMap(post => Observable.from(API.getUser(post.authorId))
 .map(user => Actions.setPost({
 post,
 user
 })
 )
 ) 
 )

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情境三：call ⼀一⼤大堆 API /api/posts
 /api/users/:id

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情境三：call ⼀一⼤大堆 API action$.ofType(GET_POSTS).switchMap(action => Observable.from(API.getPosts())
 .switchMap(posts =>
 Observable.of(...posts)
 .mergeMap(item =>
 Observable.from(API.getUser(item.authorId))
 .map(user => ({ ...item,
 user
 }))
 , 10)
 )
 )
 .toArray()
 .map(posts => Actions.setPost(posts)
 )

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情境三：call ⼀一⼤大堆 API action$.ofType(GET_POSTS).switchMap(action => Observable.from(API.getPosts())
 .switchMap(posts =>
 Observable.of(...posts)
 .mergeMap(item =>
 Observable.from(API.getUser(item.authorId))
 .map(user => ({ ...item,
 user
 }))
 , 10)
 )
 )
 .toArray()
 .map(posts => Actions.setPost(posts)
 )

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情境三：call ⼀一⼤大堆 API action$.ofType(GET_POSTS).switchMap(action => Observable.from(API.getPosts())
 .switchMap(posts =>
 Observable.of(...posts)
 .mergeMap(item =>
 Observable.from(API.getUser(item.authorId))
 .map(user => ({ ...item,
 user
 }))
 , 10)
 )
 )
 .toArray()
 .map(posts => Actions.setPost(posts)
 )

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情境三：call ⼀一⼤大堆 API action$.ofType(GET_POSTS).switchMap(action => Observable.from(API.getPosts())
 .switchMap(posts =>
 Observable.of(...posts)
 .mergeMap(item =>
 Observable.from(API.getUser(item.authorId))
 .map(user => ({ ...item,
 user
 }))
 , 10)
 )
 )
 .toArray()
 .map(posts => Actions.setPost(posts)
 )

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情境三：call ⼀一⼤大堆 API action$.ofType(GET_POSTS).switchMap(action => Observable.from(API.getPosts())
 .switchMap(posts =>
 Observable.of(...posts)
 .mergeMap(item =>
 Observable.from(API.getUser(item.authorId))
 .map(user => ({ ...item,
 user
 }))
 , 10)
 )
 )
 .toArray()
 .map(posts => Actions.setPost(posts)
 )

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