前端Rollup RxJs響應式編程實踐

響應式編程

以下概念介紹，基於 node v10.16.3 版本進行。不滿足條件的，請移步 google or 度娘。

概念介紹

const a = 1,b = 2;
const c = a  b;

響應式編程，當a,b再次變化時，c會再次做出修改。

背景

• RxJS是一個用於使用Observables進行響應式編程的庫
• 可簡化編寫異步或基於回調的代碼

本地環境搭建

• node
• npm script
• rollup

 npm install --global rollup

• rxjs

 npm install rxjs

• es6 語法，利用tree-shaking ，縮減代碼

使用

hello-world 之123

import { of } from 'rxjs';
import { map } from 'rxjs/operators';
of(1,2,3).subscribe(res => {
    console.log(res);
});

rollup打包→ bundle.js → node bundle.js，連續輸出123

rollup main.js --file bundle.js --format cjs

'use strict';

var rxjs = require('rxjs');
require('rxjs/operators');

rxjs.of(1,2,3).subscribe(res => {
    console.log(res);
});

優化rollup配置

創建rollup.config.js

export default {
  input: 'main.js',
  output: {
    file: 'bundle.js',
    format: 'cjs'
  }
};

rollup -c rollup.config.js 

npm script支持

package.json

 {
 "name": "rxjs-demo",
  "version": "1.0.0",
  "description": "",
  "main": "test.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "build":"rollup -c", // 默認配置 rollup --config  rollup.config.js
    "start":"npm run build && node bundle.js"   // && 是繼發，& 是併發
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "rxjs": "^6.5.3"
  }
}

最終的運行如下：

npm start 

Rxjs讀取package.json字段version

// install plugin
npm install --save-dev rollup-plugin-json

// rollup.config.js
import json from 'rollup-plugin-json';
export default {
    input: 'main.js',
    output: {
        file: 'bundle.js',
        format: 'cjs'
    },
    plugins:[json()]
};

// main.js
import { of } from 'rxjs';
import { map } from 'rxjs/operators';
import { version } from './package.json';

of(1,2,3,version).subscribe(res => {
    console.log(res);
});

pipe管道在輸出前修改數據

import { of } from 'rxjs';
import { map } from 'rxjs/operators';
import { version } from './package.json';

of(1,2,3,version).pipe(map(item => item   ' through pipe use map'))
.subscribe(res => {
    console.log(res);
});

用Observable改寫of

其中，可以看到observable屬於異步執行。

import { of,Observable } from 'rxjs';
import { map } from 'rxjs/operators';
import { version } from './package.json';

//through pipe 
// of(1,2,3,version).pipe(map(item => item   ' through pipe use map'))
// .subscribe(res => {
//     console.log(res);
// });

console.log("before observable....");
const publisher$ = new  Observable(suber => {
    console.log("in observable....");
    suber.next(1);
    suber.next(2);
    suber.next(3);
    suber.next(version);
});
console.log("after observable....");
publisher$.pipe(map(item => item   ' through pipe use map')).subscribe(res => {
    console.log(res);
});

subscribe訂閱幾次，通知執行幾次，而不是僅消費一次

console.log("before observable....");
const publisher$ = new  Observable(suber => {
    console.log("in observable....");
    suber.next(1);
    suber.next(2);
    suber.next(3);
    suber.next(version);
});
console.log("after observable....");
publisher$.pipe(map(item => item   ' through pipe use map')).subscribe(res => {
    console.log(res);
});
publisher$.subscribe(res => {
    console.log("subscribe second..."   res);
});

hot subscribe - 與時間先後有關，訂閱內容差

import { of,Observable } from 'rxjs';
import { map } from 'rxjs/operators';
import { version } from './package.json';

let count = 0;
console.log("before observable....");
const publisher$ = new  Observable(suber => {
    console.log("in observable....");
    setInterval(() => {
        count  ;
        suber.next(count);
    }, 100);
});
console.log("after observable....");
publisher$.pipe(map(item => 'first ...'  item)).subscribe(res => {
    console.log(res);
});

setTimeout(() => {
    const publisher2$ = new Observable(suber => {
        setInterval(() => {
            suber.next(count);
        }, 100);
    });
    publisher2$.subscribe(res => {
        console.log("second ..."   res);
    }); 
}, 1000);

cold subscribe -- 時間先後無關，內容無差異

import { of,Observable } from 'rxjs';
import { map } from 'rxjs/operators';
import { version } from './package.json';


console.log("before observable....");
const publisher$ = new  Observable(suber => {
    console.log("in observable....");
    setInterval(() => {
        let count = 0;
        count  ;
        suber.next(count);
    }, 100);
});
console.log("after observable....");
publisher$.pipe(map(item => 'first ...'  item)).subscribe(res => {
    console.log(res);
});

setTimeout(() => {
    const publisher2$ = new Observable(suber => {
        setInterval(() => {
            let count = 0;
            count  ;
            suber.next(count);
        }, 100);
    });
    publisher2$.subscribe(res => {
        console.log("second ..."   res);
    }); 
}, 1000);

observable狀態終止

import { of,Observable } from 'rxjs';
import { map } from 'rxjs/operators';
import { version } from './package.json';


const publiser$ = new Observable(suber => {
    suber.next(1);
    suber.next(2);
    suber.next(3);
    suber.next(version);
    // suber.complete();
    suber.error();
});
publiser$.subscribe({
    next:res => {
        console.log(`next ...${res}`);
    },
    complete:() => {
        console.log("complete done....");
    },
    error: () => {
        console.log("error occur....");
    }
});

停止訂閱，釋放資源，但狀態沒有終止

import { of,Observable } from 'rxjs';
import { map } from 'rxjs/operators';
import { version } from './package.json';


const publiser$ = new Observable(suber => {
    let count = 0;
    const timer = setInterval(() => {
       suber.next(count);
             count  ;
    },400);
    //suber.next(1);
    // suber.complete();
    // suber.error();
    return {
        unsubscribe:() => {
            console.log("stop push data....");
            clearInterval(timer);
        }
    }
});
const unsuber = publiser$.subscribe({
    next:res => {
        console.log(`next ...${res}`);
    },
    complete:() => {
        console.log("complete done....");
    },
    error: () => {
        console.log("error occur....");
    }
});

setTimeout(() => {
    unsuber.unsubscribe();
},2000);

利用rxjs自帶操作符優化上述的取消訂閱

import { of,Observable, interval } from 'rxjs';
import { map } from 'rxjs/operators';
import { version } from './package.json';


const publiser$ = interval(400);
const unsuber = publiser$.subscribe({
    next:res => {
        console.log(`next ...${res}`);
    },
    complete:() => {
        console.log("complete done....");
    },
    error: () => {
        console.log("error occur....");
    }
});

setTimeout(() => {
    unsuber.unsubscribe();
},2000);

雙重身份的SubJect

import { of,Observable, interval,Subject } from 'rxjs';
import { map } from 'rxjs/operators';
import { version } from './package.json';

const sub = new Subject();
sub.pipe(map(res => 'first ...' res)).subscribe((res) => {
    console.log("sub one...",res);
});
sub.subscribe({
    next:(res) => {
        console.log(`second...${res}`);
    }
});
sub.next(1);
sub.next(2);

import { of,Observable, interval,Subject ,from} from 'rxjs';
import { map } from 'rxjs/operators';
import { version } from './package.json';

const sub = new Subject();
sub.pipe(map(res => 'first ...' res)).subscribe((res) => {
    console.log("sub one...",res);
});
sub.subscribe({
    next:(res) => {
        console.log(`second...${res}`);
    }
});
// sub.next(1);
// sub.next(2);
const publisher$ = from([1,2,3]);
publisher$.subscribe(sub);

參考文獻

RxJS

RxJS 操作符

阮一峯的網絡日誌 npm scripts 使用指南

本文作者：前端首席體驗師(CheongHu)

聯繫郵箱：[email protected]