Make object keys private/invisible via Symbols

1// import from another module
2var type = Symbol(); 
3
4class Telemetry {
5   constructor(val,typ){
6      this.value = val;
7      this[type] = typ;  //private
8   }
9   emit(){
10       console.log(`Telemetry type is ${this[type]}, value is ${this.value}`);
11   }
12}
13
14const tel = new Telemetry(200, 'xpto');
15console.log(tel);
16
17// --------------------------------------
18// Read type (only if the symbol is know)
19console.log(tel[type]);
20
21// Try to Hack
22console.log(JSON.stringify(tel)); // {"value": 200}
23console.log(Object.keys(tel));