Types in TypeScript

The basic types are called primitives: 

• boolean
• number (which represents integers and floating points)
• string  

There is also:

•  BigInt (ES2020+) to represent whole numbers larger than 2^53 -1, and
•  symbol to create unique identifiers

Starting with ES2015, symbol is a primitive type, whose values are created by calling the Symbol constructor.

Examples:

let sym1 = Symbol();

let sym2 = Symbol("keyname");

Symbols are immutable and unique, which can result in what may be initially feel like strange behaviour, but on reflection makes sense.

let sym2 = Symbol("key");

let sym3 = Symbol("key");

sym2 === sym3; // triple equality - false, Symbols are unique.