Node.js: ndjson の使い方

こちらにあるデータをサンプルとして使います。
新型コロナワクチンの接種状況（高齢者等）
「都道府県別接種回数詳細」 です。

prefecture.ndjson　をダウンロードします。
これを、栃木県の　2021-06-05 だけのものにします。

awk '/"prefecture":"09"/{print $0}' prefecture.ndjson > tochigi.ndjson
awk '/"date":"2021-06-05"/{print $0}' tochigi.ndjson > tochigi_jun05.ndjson

tochigi_jun05.ndjson

{"date":"2021-06-05","prefecture":"09","gender":"F","age":"-64","medical_worker":false,"status":1,"count":28}
{"date":"2021-06-05","prefecture":"09","gender":"F","age":"-64","medical_worker":false,"status":2,"count":2}
{"date":"2021-06-05","prefecture":"09","gender":"F","age":"65-","medical_worker":false,"status":1,"count":1380}
{"date":"2021-06-05","prefecture":"09","gender":"F","age":"65-","medical_worker":false,"status":2,"count":245}
{"date":"2021-06-05","prefecture":"09","gender":"M","age":"-64","medical_worker":false,"status":1,"count":28}
{"date":"2021-06-05","prefecture":"09","gender":"M","age":"-64","medical_worker":false,"status":2,"count":4}
{"date":"2021-06-05","prefecture":"09","gender":"M","age":"65-","medical_worker":false,"status":1,"count":1031}
{"date":"2021-06-05","prefecture":"09","gender":"M","age":"65-","medical_worker":false,"status":2,"count":192}
{"date":"2021-06-05","prefecture":"09","gender":"U","age":"UNK","medical_worker":false,"status":1,"count":1}

必要なライブラリーのインストール

sudo npm install -g ndjson

ex01.js

# ! /usr/bin/node
// ---------------------------------------------------------------
//	ex01.js
//
//						Jun/06/2021
// ---------------------------------------------------------------
'use strict'

const ndjson = require('ndjson')
var fs = require("fs")

const file_in = 'tochigi_jun05.ndjson'

fs.createReadStream(file_in)
  .pipe(ndjson.parse())
  .on('data', function(obj) {
    // obj is a javascript object
	console.log(obj)
  })

// ---------------------------------------------------------------

実行

export NODE_PATH=/usr/lib/node_modules
./ex01.js