How to escape special chars in JSON

Sample code on PuckJS that is causing issues if not escaped when sending to a Espruino device after two times E.toJS

var aJS5 = {txt : "012345\nabcde\näöüß"};
var saJS5 = E.toJS(aJS5);  
//"{txt:\"012345\\nabcde\\n\\xE4\\xF6\\xFC\\xDF\"}"
var sa2JS5 =  E.toJS(saJS5);
// "{txt:\"012345\\nabcde\\n\\xE4\\xF6\\xFC\\xDF\"}"  // same
var COMMAND = `\x03\x10transfer(${sa2JS5})\n`;
// transfer("{txt:\"012345\\nabcde\\n\\xE4\\xF6\\xFC\\xDF\"}")  <- cause syntax error


var saJS5e =  E.toJS(aJS5).replace(/\\n/g,'\\\\n').replace(/\\x/g,'\\\\x'); 
// "{txt:\"012345\\\\nabcde\\\\n\\\\xE4\\\\xF6\\\\xFC\\\\xDF\"}";
var COMMAND = `\x03\x10transfer(${saJS5e})\n`;
// "\3\x10transfer({txt:\"012345\\\\nabcde\\\\n\\\\xE4\\\\xF6\\\\xFC\\\\xDF\"})\n"; // <- no error