Symbols

Symbols are a primitive data type that represents an immutable value which is guaranteed to be globally unique throughout the lifetime of the program.

Symbols can be used as keys for object properties and provide a way to create non-enumerable properties.

const key1: symbol = Symbol('key1');
const key2: symbol = Symbol('key2');

const obj = {
    [key1]: 'value 1',
    [key2]: 'value 2',
};

console.log(obj[key1]); // value 1
console.log(obj[key2]); // value 2

In WeakMaps and WeakSets, symbols are now permissible as keys.