Will typescript target es6 have problem with ionic 2?

I want to use Proxy on a customized class called ObservableList which contains an Array. Since Proxy is available only after ES6, I set the target to be es6 in tsconfig.json. I wonder if it would have any compatible problem with app generated with ionic 2, like if the web view version on a user’s mobile is too low.

Or, is there any alternatives for Proxy? My requirement is to get updated (rather than get noticed) for observers once ObservableList changes, so that the observers are always consist with observable with some filtering or mapping method.

var activities = new ObservableList(['reading', 'swimming']);
var sAct = activities.filter(function(v) {
  return v[0] === 's';
});
// expect sAct.list to be ['swimming']
var meAct = activities.map(function(v) {
  return 'I am ' + v;
});
// expect meAct.list to be ['I am reading', 'I am swimming']

activities.list.push('smiling');
console.log(sAct.list, meAct.list);
// expect sAct.list to be ['swimming', 'smiling']
// expect meAct.list to be ['I am reading', 'I am swimming', 'I am smiling']

activities.list[1] = 'snoopying';
console.log(sAct.list, meAct.list);
// expect sAct.list to be ['swimming', 'snoopying']
// expect meAct.list to be ['I am reading', 'I am snoopying', 'I am smiling']

My implementation with proxy is available at https://jsfiddle.net/ovilia/tLmbptr0/3/

IMHO the app won’t work on any real device if you set the target to es6 in tsconfig.json, e.g. even the latest iOS 9 supports only a bit over 50% of the ES6 features and the other mobile OSes seem to have even lower ES6 support.

Does anyone know if this information is still valid?