Question

do / tap

函数签名: do(nextOrObserver: function, error: function, complete: function): Observable

Transparently perform actions or side-effects, such as logging.

透明地执行操作或副作用，比如打印日志。

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If you are using as a pipeable operator, do is known as tap!

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示例

示例 1: 使用 do 输出日志

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { of } from 'rxjs';
import { tap, map } from 'rxjs/operators';

const source = of(1, 2, 3, 4, 5);
// 使用 tap 透明地打印 source 中的值
const example = source.pipe(
  tap(val => console.log(`BEFORE MAP: ${val}`)),
  map(val => val + 10),
  tap(val => console.log(`AFTER MAP: ${val}`))
);

// 'tap' 并不转换值
// 输出: 11...12...13...14...15
const subscribe = example.subscribe(val => console.log(val));

其他资源

• do :newspaper: - 官方文档
• 使用 do 打印流 :video_camera: :dollar: - John Linquist
• 工具操作符: do :video_camera: :dollar: - André Staltz

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源码: https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/do.ts