arcbyte/JavaScript
LibraryJavaScriptDates and Internationalization

Dates and Internationalization

Represent instants safely and format dates, numbers, and lists for different locales.

Updated Tested with ECMAScript 2026 and Intl

A JavaScript Date represents an instant as milliseconds from the Unix epoch. Time-zone and calendar formatting belong at the display boundary.

Parse explicit input

dates.js
const published = new Date("2026-08-13T16:00:00Z");
if (Number.isNaN(published.getTime())) throw new TypeError("Invalid date");
console.log(published.toISOString());

Use ISO 8601 with an explicit offset or Z. Ambiguous date-only or locale-formatted strings can be interpreted differently than expected.

Format for a locale

format.js
const date = new Intl.DateTimeFormat("en-US", {
  dateStyle: "long",
  timeStyle: "short",
  timeZone: "America/New_York",
}).format(published);

const duration = new Intl.NumberFormat("zh-CN").format(112);
const list = new Intl.ListFormat("en", { type: "conjunction" }).format(["HTML", "CSS", "JavaScript"]);

Keep this

Store instants in an unambiguous format, validate parsing, and use Intl for human-readable output.

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