Symbols are primatives for unique values in javascript
> Symbol(value) returns a unique symbol
> Symbol.for(value) returns a unique symbol, but two calls using the
same key will return the same symbol, within the scope
They can be useful because they are hidden from most iteration functions.
For ex, if you want to add a value to an object that you got back from a
third-party api. This will make sure your value doesn't appear in iteration
functions, and also won't require changing how the api is set up
let sym1 = Symbol()
let sym2 = Symbol('foo')
let sym3 = Symbol('foo')// two symbols with the same description
const value1 = Symbol('hello');
const value2 = Symbol('hello');
console.log(value1 === value2); // false// two symbols with the same description
const value1 = Symbol('hello');
const value2 = Symbol('hello');
let sym2 = Symbol('foo')
let sym3 = Symbol('foo')
console.log(Symbol(sym2==sym3)); /*false, symbols are guaranteed to be unique*/