Хорошо, вы можете использовать функцию сортировки, но помните, что она изменяет исходный массив.
const someArr = [{"_id":"5c585ed5a9a5b931c3057d48","exchange":"Poloniex","totaleth":-338,"dt":"2019-02-04T15:48:37.232Z","__v":0},{"_id":"5c585ed5a9a5b931c3057d47","exchange":"Bitrex","totaleth":-227,"dt":"2019-02-04T15:48:37.222Z","__v":0},{"_id":"5c585ed5a9a5b931c3057d46","exchange":"Gemini","totaleth":86,"dt":"2019-02-04T15:48:37.220Z","__v":0},{"_id":"5c585ed5a9a5b931c3057d45","exchange":"Bitfinex","totaleth":-373,"dt":"2019-02-04T15:48:37.219Z","__v":0},{"_id":"5c585ed4a9a5b931c3057d44","exchange":"Binance","totaleth":6531,"dt":"2019-02-04T15:48:36.586Z","__v":0}];
console.log(
someArr.sort((a, b) => {
return a.totaleth - b.totaleth;
})
);