How to escape special chars in JSON

Got some special chars in JSON that needed to be escapes.

var aJS = {txt : "012345\nabcde\näöüß"};
var s_aJS5 = E.toJS(aJS);
// "{txt:\"012345\\nabcde\\n\\xE4\\xF6\\xFC\\xDF\"}";

// but in some cases additional encoding is required 
var s_aJS5_e = E.toJS(aJS).replace(/\\n/g,'\\\\n').replace(/\\x/g,'\\\\x'); 
//  "{txt:\"012345\\\\nabcde\\\\n\\\\xE4\\\\xF6\\\\xFC\\\\xDF\"}";

Is there a Espruino function for this, or could this be another candidate for StringDecoders?