Primitive types in TypeScript

Annotating the basic types, arrays, and tuples.

const name: string = "typestar";
const count: number = 42;
const ready: boolean = true;
const tags: string[] = ["code", "typing"];
const pair: [string, number] = ["score", 95];

let maybe: string | undefined;
const values: readonly number[] = [1, 2, 3];

function describe(input: string | number): string {
  return typeof input === "string" ? input.trim() : input.toFixed(1);
}

How it works

1. Annotations follow the name after a colon.
2. [string, number] is a fixed-length tuple.
3. A union parameter is narrowed with typeof.

Keywords and builtins used here

• boolean
• const
• function
• let
• number
• readonly
• return
• string

The run, in numbers

Lines

12

Characters to type

376

Tokens

104

Three-star pace

85 tpm

At the three-star pace of 85 tokens a minute, this run takes about 73 seconds.

Type this snippet

Step 1 of 4 in Primitives & literals, step 1 of 23 in Types & annotations.

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