3-ts-data-types-annotations.md

Type annotations for the complete set of basic types

Primitive Types

• isComplete: boolean = false;: This variable isComplete is of type boolean and is initialized with the value false.
• stock: number = 10;: This variable stock is of type number and is initialized with the value 10.
• greeting: string = "Welcome!";: This variable greeting is of type string and is initialized with the value "Welcome!".
• largeNumber: bigint = 900719925474099100n;: This variable largeNumber is of type bigint and is initialized with a large number.
• unique: symbol = Symbol("unique");: This variable unique is of type symbol and is initialized with a unique symbol.

Special Types

• nothingHere: null = null;: This variable nothingHere is of type null and is assigned the value null.
• notAssigned: undefined;: This variable notAssigned is declared but not assigned a value, hence its type is undefined.

Structural Types

• interface Product { name: string; price: number; }: This defines an interface Product with name and price properties.
• product: Product = { name: "Tablet", price: 500 };: This variable product is of type Product and represents a product object with a name and a price.
• colors: string[] = ["Red", "Green", "Blue"];: This variable colors is an array of strings initialized with colors.
• scores: number[] = [85, 90, 78];: This variable scores is an array of numbers initialized with scores.

Utility Types (some common examples)

• anythingGoes: unknown = 42;: This variable anythingGoes is of type unknown and is assigned the value 42.
• neverReturns: never;: This variable neverReturns is declared but never assigned a value, indicating it will never have a value.
• flexibleType: number | string;: This variable flexibleType can hold either a number or a string.

Function with Type Annotations

function calculateArea(width: number, height: number): number {
  return width * height;
}

Key Points:

• Type annotations in TypeScript allow you to explicitly specify the type of a variable.
• Primitive types include boolean, number, string, bigint, and symbol.
• Special types such as null and undefined represent absence of value and uninitialized variables, respectively.
• Structural types can be defined using interfaces to specify the structure of objects.
• Arrays in TypeScript can be defined using square brackets followed by the type of elements.
• Utility types provide additional features for working with types, such as unknown and never.
• Functions can also have type annotations for parameters and return types, ensuring type safety and clarity.