TypeScript: Type Syntax

Type Declaration Syntax

• The first thing you shoud do is add types to function parameters.
• This is the most simple, useful.

the form is:

:TypeSpec

placed after a variable name.

Example

// vector addition
const f_vec_add =
  ((
    [a1, a2]: [number, number],
    [b1, b2]: [number, number],
  ): [number, number] => [a1 + b1, a2 + b2]);

const f_vec_length = ((v: number[]) => Math.hypot(...v));

Type Syntax

here are the syntax for the type spec.

Type Spec Syntax for JavaScript Primitive Types

• string
• number
• boolean
• any

Array Type

• TypeSpec[]

Object Type

• { …: TypeSpec; …: TypeSpec … }

Optional Property

add a question mark to the end of variable name.

• { …: TypeSpec; … ?: TypeSpec })

Union Types

Union Types means one or the other.

• TypeSpec | TypeSpec

can be more than two items.