Explain the symbol type in TypeScript.

Symbols were introduced in ES6 and are supported by TypeScript. Similar to numbers and strings, symbols are primitive types. You can use Symbols to create unique properties for objects.

You can create symbol values by calling the Symbol() constructor, optionally providing a string key.

let foo = Symbol();
let bar = Symbol("bar"); // optional string key

A key characteristic of symbols is that they are unique and immutable.

let foo = Symbol("foo");
let newFoo = Symbol("foo");

let areEqual = foo === newFoo;
console.log(areEqual);  // false, symbols are unique