ES6 In Depth - Symbols

Symbols aren’t exactly like anything else. They’re immutable once created. You can’t set properties on them (and if you try that in strict mode, you’ll get a TypeError). They can be property names. These are all string-like qualities. On the other hand, each symbol is unique, distinct from all others (even others that have the same description) and you can easily create new ones. These are object-like qualities. ES6 symbols are similar to the more traditional symbols in languages like Lisp and Ruby, but not so closely integrated into the language. In Lisp, all identifiers are symbols. In JS, identifiers and most property keys are still considered strings. Symbols are just an extra option.