do / tap

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。

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

示例

示例 1: 使用 do 输出日志

( jsBin |
jsFiddle )

import { of } from 'rxjs/observable/of';
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 - 官方文档
• 使用 do 打印流 - John Linquist
• 工具操作符: do - André Staltz

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