How to escape special chars in JSON

Sorry, I'm not sure I understand...

Sample code on Mac that is causing no issues when sending to a Espruino device after two time JSON5.stringify() like this:

var noble = require('@abandonware/noble');
const JSON5 = require('json5');
var  aJS = {txt : "012345\nabcde\näöüß"};
var  saJS5 = JSON5.stringify(aJS);    
// {txt:'012345\nabcde\näöüß'}
var sa2JS5 =  JSON5.stringify(saJS5);
// {txt:'012345\\nabcde\\näöüß'}
var COMMAND = `\x03\x10transfer(${sa2JS5})\n`;
// transfer("{txt:'012345\\nabcde\\näöüß'}")

// use  https://www.espruino.com/Interfacing  Node.js / JavaScript
// added some seconds before calling disconnect to catch more data

sample code on PuckJS

transfer = function (saJS5) {
        var aJS5;
        try {
            aJS5 = eval('('+saJS5+')');
        } catch(e){
            console.log("error in eval:",e);
        }
}