Rx.Observable.of(1, 2, 3, 4, 5)

  // `do`内の関数（処理）は Observable に影響を与えない

  .do(v => console.log(`map を実行前: ${v}`))

  .map(v => v * 10)

  .do(v => console.log(`map を実行後: ${v}`))

  .subscribe(

    x => console.log(`next: ${x}`),

    error => console.error(`error: ${error}`),

    () => console.log("complete")

  );

// => "map を実行前: 1"

// => "map を実行後: 10"

// => "next: 10"

// => "map を実行前: 2"

// => "map を実行後: 20"

// => "next: 20"

// => "map を実行前: 3"

// => "map を実行後: 30"

// => "next: 30"

// => "map を実行前: 4"

// => "map を実行後: 40"

// => "next: 40"

// => "map を実行前: 5"

// => "map を実行後: 50"

// => "next: 50"

// => "complete"