Dates Intl

By the end of this lesson you'll create, read, and format dates correctly — and show times, currencies, and "3 hours ago" the way each user's country expects.

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Part of the free JavaScript course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

📚 Prerequisites: You should be comfortable with variables and functions . Knowing how objects and methods work will help, since a date is an object with methods.

💡 Running Code Locally: While this online editor runs real JavaScript, some advanced examples may have limitations. For the best experience:

🕰️ Real-World Analogy: A Date is like the single counter on a stopwatch that started ticking at midnight on Jan 1, 1970 (UTC) :

A Date is JavaScript's built-in type for a moment in time. It does not store a time zone. It stores a single number: the milliseconds since the epoch (midnight, Jan 1 1970, UTC). Every other thing you see — local time, ISO strings, formatted text — is calculated from that number.

You create "now" with new Date() , read the raw number with getTime() , and get a universal string with toISOString() .

There are three reliable ways to build a date. The safest take the guesswork out of which time zone JavaScript should assume. Notice the month is zero-indexed in the numeric constructor — 0 is January, 11 is December.

Each piece has a get method and a matching set method: getFullYear() , getMonth() , getDate() (day of month), getDay() (day of week, 0 = Sunday), getHours() , and so on. The set methods mutate the date in place and conveniently roll over — adding a day to Jan 31 lands on Feb 1.

Remember: the month in Date.UTC() is zero-indexed. Fill in the blanks.

A timestamp is just that millisecond number. Because it's plain arithmetic, adding fixed durations (minutes, hours) is reliable. Date.now() gives the current timestamp directly. To add calendar units like days or months, prefer the set methods, which respect month lengths and daylight saving.

Never build a display string by hand. Intl.DateTimeFormat takes a locale (like "en-US" or "en-GB" ) and an options object, then prints the date the way that country writes it — correct order, month names, and 12- vs 24-hour clock. Pass timeZone to control which zone it renders in.

The same family formats numbers. With style: "currency" and a currency code, Intl.NumberFormat adds the right symbol, decimals, and grouping for the locale. This is how you show prices correctly to a global audience.

For feeds and notifications, show relative time. Negative numbers are the past, positive are the future. With numeric: "auto" it even says "yesterday" and "tomorrow" where a language has those words.

Use Intl.NumberFormat to print a euro price for a French audience.

Now with the scaffolding removed. Work from the comment outline only.

Store the instant in UTC; convert only when you display . Pass an IANA zone name (like "America/New_York" ) to timeZone and the formatter handles the offset and daylight saving for you.

📦 A Note on Date Libraries: The built-in Date is fine for the basics, but it is mutable and quirky. Two things worth knowing:

You can now handle dates the way production apps do — accurately, and in any language. 🌍

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