Function Type Expressions

The simplest way to describe a function is with a function type expression.
These types are syntactically similar to arrow functions:

function (: (: string) => void) {
  ('Hello World')
}

function (: string) {
  .()
}

()

Imagine we have a function called padLeft.

function (: number | string, : string): string {
  throw new ('Not implemented yet!')
}

The TypeScript Handbook

Source Code

The primitives: string, number, and boolean

JavaScript has three very commonly used primitives: string, number, and boolean.

number: JavaScript does not have a special runtime value for integers, so there’s no equivalent to int or float - everything is simply number

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