How to use

_flatten

function

in

lodash

const symbols = details.map(d => `t${d.pair.toUpperCase()}`)
const timeFrames = ['1m', '5m', '30m', '1h', '6h']
const keys = _flatten(symbols.map(s => {
 return timeFrames.map(tf => `trade:${tf}:${s}`)
}))

return _flatten(responses)