１．Gweiで求めた値をGweiもしくはETHで表示する
・小数点以下の表示の設定
・symbol
・pattern

２．require
・currency.js

３．code

    const currency = require('currency.js');
・・・
    let t = parseFloat(total) / 1000000000;

    const CURRENCY_ETH =  {
        "formatWithSymbol" : true,
        "symbol" : "ETH",
        "separator" : ",",
        "decimal" : ".",
        "precision" : 9,
        "pattern" : "# !"
    }
    const CURRENCY_GWei =  {
        "formatWithSymbol" : true,
        "symbol" : "Gwai",
        "separator" : ",",
        "decimal" : ".",
        "precision" : 0,
        "pattern" : "# !"
    }
    let msg;
    if( total >1000) {
        msg ={ total:  currency(t.toString(),CURRENCY_Gwai).format(true) }
    } else {
        msg ={ total:  currency(total.toString(),CURRENCY_ETH).format(true) }
    }
    console.log(msg.total)