Localizing Dates and Times with Moment.js

Introduction

Moment.js is a popular JavaScript library for parsing, validating, manipulating, and formatting dates and times. A crucial aspect of building internationalized applications is the ability to display dates and times in a user’s preferred language and format. This tutorial will guide you through the process of localizing your Moment.js dates and times, enabling you to create a more user-friendly experience for a global audience.

Setting the Locale

Moment.js provides a locale() function to set the language for date and time formatting. It’s important to understand how this function behaves when used globally versus on individual Moment objects.

Global Locale Setting

To set the default locale for all subsequent Moment objects, you call moment.locale(). This changes the default formatting for any dates created after this call.

moment.locale('de'); // Sets the global locale to German
var now = moment();
console.log(now.format('LLLL')); // Output will be in German

Instance-Specific Locale Setting

You can also set the locale for a specific Moment object without affecting the global default. This is useful when you need to display dates in multiple languages within the same application.

var march = moment('2017-03');
console.log(march.format('MMMM')); // Output: 'March' (English)

moment.locale('de'); // Set global locale to German
console.log(march.format('MMMM')); // Still 'March' - instance isn't updated!

var deMarch = moment('2017-03'); // Create a *new* moment object
console.log(deMarch.format('MMMM')); // Output: 'März' (German)

march.locale('es'); // Change locale of the *existing* instance
console.log(march.format('MMMM')); // Output: 'Marzo' (Spanish)

Loading Locale Files

Before you can use a specific locale, you need to load the corresponding locale file. These files contain the translations and formatting rules for that language.

Using Bundlers (Webpack, Parcel, Rollup)

Modern JavaScript projects typically use bundlers to manage dependencies and optimize code. With bundlers, you can import the locale file directly into your code.

import moment from 'moment';
import 'moment/locale/fr'; // Import the French locale
import 'moment/locale/es'; // Import the Spanish locale

moment.locale('fr'); // Set the locale to French
var now = moment();
console.log(now.format('LLLL')); // Output will be in French

Using Script Tags (CDN or Local Files)

If you’re not using a bundler, you can include the Moment.js core and locale files directly in your HTML using <script> tags.

<script src="moment.js"></script>
<script src="moment/locale/de.js"></script>

<script>
  moment.locale('de');
  var now = moment();
  console.log(now.format('LLLL')); // Output will be in German
</script>

Important: Ensure that you load the core moment.js file before loading any locale files.

Loading all Locales

Moment.js provides a way to load all locales at once, which might be helpful in some cases. However, this will significantly increase the size of your bundle.

import moment from 'moment';
import 'moment/min/locales'; // Loads all locales

moment.locale('fr');

Using this approach might be useful if you dynamically switch between numerous locales.

Available Locales

Moment.js supports a wide range of locales. You can find a complete list in the official Moment.js documentation: https://momentjs.com/docs/#/i18n/

Best Practices

Load only the locales you need: Avoid loading all locales to minimize bundle size.
Set the locale early: Set the global locale as early as possible in your application to ensure consistent formatting.
Consider user preferences: Ideally, allow users to select their preferred language and store this preference for future sessions.
Test thoroughly: Test your localization with various locales to ensure that dates and times are displayed correctly in all languages.