getCandles (key) {
    return this._candles[key] || []
  }
Fetch a reference to the full set of synced candles for the specified key.
Set `managedCandles: true` in the constructor to use.

@param {string} key - key for candle set
@returns {Array} candles - empty array if none exist
@example
  const ws = new WSv2({ managedCandles: true })

  ws.on('open', async () => {
      ws.onCandles({ key: 'trade:1m:tBTCUSD' }, () => {
        const candles = ws.getCandles('trade:1m:tBTCUSD')

        if (!candles) return

        console.log('%d candles in dataset', candles.length)
      })

      ws.subscribeCandles({ key: 'trade:1m:tBTCUSD' })
  })

  await ws.open()