TypeScript Data Types

Primitive Types

TypeScript supports all basic types found in JavaScript:

let age: number = 30;
let isStudent: boolean = false;
let name: string = "Alice";
let empty: null = null;
let notDefined: undefined = undefined;
let bigValue: bigint = 123n;
let uniqueId: symbol = Symbol("id");

Arrays

Arrays can be declared in two ways:

let scores: number[] = [90, 80, 70];
let names: Array<string> = ["Alice", "Bob"];

Tuples

Tuples are arrays with fixed length and known types:

let person: [string, number] = ["Alice", 30];

Each element is typed specifically, making tuples ideal for structured data.

Enums

Enums are used for named constants:

enum Direction {
  Up,
  Down,
  Left,
  Right
}

let dir: Direction = Direction.Up;

Enums improve code clarity and prevent magic numbers or strings.

Special Types: any, unknown, void, never

let anything: any = 5;
anything = "hello";

let unsure: unknown = "value"; // safer than any

function log(): void {
  console.log("Logging");
}

function error(): never {
  throw new Error("Something went wrong");
}

any: disables type checking.
unknown: requires checking before use.
void: used in functions that return nothing.
never: for functions that never return.

Type Assertions

Used to tell the compiler the exact type of a variable:

let value: any = "Hello";
let strLength: number = (value as string).length;

// or using angle bracket
let length2: number = (<string>value).length;

Best Practices

Use precise types over any for better safety.
Take advantage of type inference but be explicit when needed.
Avoid overusing type assertions unless necessary.

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