stacker.news/api/resolvers/chainFee.js

import lndService from 'ln-service'
import lnd from '../lnd'

const cache = new Map()
const expiresIn = 1000 * 30 // 30 seconds in milliseconds

async function fetchChainFeeRate () {
  let chainFee = 0
  try {
    const fee = await lndService.getChainFeeRate({ lnd })
    chainFee = fee.tokens_per_vbyte
  } catch (err) {
    console.error('fetchChainFee', err)
  }
  cache.set('fee', { fee: chainFee, createdAt: Date.now() })
  return chainFee
}

async function getChainFeeRate () {
  if (cache.has('fee')) {
    const { fee, createdAt } = cache.get('fee')
    const expired = createdAt + expiresIn < Date.now()
    if (expired) fetchChainFeeRate().catch(console.error) // update cache
    return fee
  } else {
    fetchChainFeeRate().catch(console.error)
  }
  return 0
}

export default {
  Query: {
    chainFee: async (parent, opts, ctx) => {
      return await getChainFeeRate()
    }
  }
}