Symbol.for method allows you to register and look up global symbols by name. The first time it is called with a given key, it creates a new symbol and adds it to the registry.
let a = Symbol.for('A');
The next time you call
Symbol.for('A'), the same symbol will be returned instead of a new one (in contrast to
Symbol('A') which would create a new, unique symbol that happens to have the same description).
a === Symbol.for('A') // true
a === Symbol('A') // false