RxJS do

sample1.ts

import * as Rx from "@reactivex/rxjs";

// doオペレータで値の流れを確認
Rx.Observable.of(1, 2, 3)
	.do(value => console.log(`do[of]: (value: ${value})`))
	.filter(value => value % 2 == 0)
	.do(value => console.log(`do[filtered]: (value: ${value})`))
	.map(value => value * 2)
	.do(value => console.log(`do[mapped]: (value: ${value})`))
	.subscribe(
		value => console.log(`next: (value: ${value})`),
		error => console.log(`error: ${error}`),
		() => console.log(`complete:`));
// 実行結果
/*
do[of]: (value: 1)
do[of]: (value: 2)
do[filtered]: (value: 2)
do[mapped]: (value: 4)
next: (value: 4)
do[of]: (value: 3)
complete:
*/

sample2.ts

import * as Rx from "@reactivex/rxjs";

// doオペレータの引数はsubscribeと同じ
// completeコールバックも呼ばれる
Rx.Observable.of(2)
	.do(
		value => console.log(`do.next: (value: ${value})`),
		error => console.log(`do.error: ${error}`),
		() => console.log(`do.complete:`))
	.filter(value => value % 2 == 0)
	.subscribe(
		value => console.log(`subscribe.next: (value: ${value})`),
		error => console.log(`subscribe.error: ${error}`),
		() => console.log(`subscribe.complete:`));
// 実行結果
/*
do.next: (value: 2)
subscribe.next: (value: 2)
do.complete:
subscribe.complete:
*/

// errorコールバックも呼ばれる
Rx.Observable.throw("いきなりエラー")
	.do(
		value => console.log(`do.next: (value: ${value})`),
		error => console.log(`do.error: ${error}`),
		() => console.log(`do.complete:`))
	.filter(value => value % 2 == 0)
	.subscribe(
		value => console.log(`subscribe.next: (value: ${value})`),
		error => console.log(`subscribe.error: ${error}`),
		() => console.log(`subscribe.complete:`));
// 実行結果
/*
do.error: いきなりエラー
subscribe.error: いきなりエラー
*/