data.js

const got = require('got')
const cheerio = require('cheerio')
const { writeFile } = require('fs')

let data = []

function fetch (year, month, cb) {
  const url = `https://www.metnet.hu/?m=napi-adatok&sub=4&pid=6321&date=${
    year}-${month < 10 ? '0' + month : month}-01`
  got.get(url).then(res => {
    const $ = cheerio.load(res.body)
    const trs = $('.sblokk342 table tr')

    for (let i = 0; i < trs.length; ++i) {
      if (i === 0 || trs[i].children.length !== 13) continue
      const tds = $(trs[i]).find('td')
      const day = Number($(tds[0]).text())
      const min = Number($(tds[1]).html().replace(/ &#xFFFD;C/i, '').replace(',', '.'))
      const max = Number($(tds[2]).html().replace(/ &#xFFFD;C/i, '').replace(',', '.'))
      const avg = (min + max) / 2
      const o = {
        year: year,
        month: month,
        day, min, max, avg
      }
      data.push(o)
    }

    if (month < 12) {
      fetch(year, month + 1, cb)
    } else {
      if (year < 2015) fetch(year + 1, 1, cb)
      else cb()
    }
  }).catch(err => console.error(err))
}

fetch(2000, 4, () => {
  writeFile('data.json', JSON.stringify(data), 'utf8', err => {
    if (err) return console.error(err)
    console.log('written')
  })
})