Instantiate All At Once

import ccxt from '../../js/ccxt.js';

async function test () {

   let exchanges = { 
       "bittrex": {
           "apiKey": "YOUR_API_KEY", 
           "secret": "YOUR_SECRET",
       },
       "bitfinex": { 
           "apiKey": "YOUR_API_KEY", 
           "secret": "YOUR_SECRET"
       },
   }

   let ids = ccxt.exchanges.filter (id => id in exchanges)

   await Promise.all (ids.map (async id => {

       console.log (exchanges[id])

       // instantiate the exchange
       let exchange = new ccxt[id] (exchanges[id])
       console.log (exchange.id, exchange.apiKey)
       exchanges[id] = exchange

       // load markets
       await exchange.loadMarkets ()
       console.log (exchange.id, 'loaded')

       // check the balance
       if (exchange.apiKey) {
           let balance = await exchange.fetchBalance ()
           console.log (exchange.id, balance)
       }

       return exchange
   }))

   // when all of them are ready, do your other things
   console.log ('Loaded exchanges:', ids.join (', '))
}

test ()