Symbols
Unique and immutable data type to be used as an identifier for object properties
Syntax
let sym = Symbol('foo');
console.log(sym); //=> Symbol(foo)
//Global Symbol
sym = Symbol.for('foo');
console.log(sym); //=> Symbol(foo)
console.log(Symbol('foo') !== Symbol('foo')); //=> true
console.log(Symbol.for('foo') !== Symbol.for('foo')); //=> false