Symbol.for("key")
Checks if a symbol with the key "key" already exists in the globals symbol registry.
If yes, it returns the existing symbol, otherwise, it creates a new symbol and adds it to the global regsitery.
Symbol("key")
Always creates a new, unique symbol that is different from any other symbol.
const one = Symbol.for("key")
const two = Symbol("key")
const three = Symbol.for("key")
console.log(one === two) // false
console.log(two === three) // false
console.log(one === three) // true
console.log(three === Symbol("key")) // false