Unix Timestamp in TypeScript

TypeScript uses the same Date API as JavaScript but adds static typing. Adding explicit type annotations prevents common timestamp bugs — like accidentally mixing seconds and milliseconds — at compile time.

Code Examples

Current timestamp (seconds)

const seconds: number = Math.floor(Date.now() / 1000);

Type-annotated Unix timestamp in seconds. The number type annotation is optional but makes the intent explicit — this is seconds, not milliseconds.

Current timestamp (milliseconds)

const ms: number = Date.now();

Date.now() natively returns a number in milliseconds. In TypeScript, this is typed as number. A 13-digit value.

Branded types — prevent seconds/ms confusion

type Seconds = number & { readonly __brand: "seconds" };
type Milliseconds = number & { readonly __brand: "milliseconds" };

const toSeconds = (ms: Milliseconds): Seconds =>
  Math.floor(ms / 1000) as Seconds;

const now: Milliseconds = Date.now() as Milliseconds;
const nowSeconds: Seconds = toSeconds(now);

Advanced pattern: branded (nominal) types ensure you can't accidentally pass milliseconds where seconds are expected. The TypeScript compiler will error if you mix them.

Convert Date string to timestamp

const ts: number = Math.floor(new Date("2024-06-15T12:00:00Z").getTime() / 1000);

Parse an ISO 8601 string and convert to Unix seconds. getTime() returns milliseconds, so divide by 1000.

Convert timestamp to Date

const date: Date = new Date(seconds * 1000);
const iso: string = date.toISOString();

Multiply seconds by 1000 to get milliseconds before passing to the Date constructor. toISOString() returns a UTC string like 2024-02-22T00:00:00.000Z.

Note

TypeScript's number type doesn't distinguish between seconds and milliseconds — both are just number. The branded type pattern above is an advanced but powerful technique for preventing this class of bug in large codebases. For simpler code, a naming convention (tsSeconds, tsMs) is usually sufficient.

Related Languages

Unix timestamp in JavaScript →Unix timestamp in Go →Unix timestamp in Java →

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