.toLocaleString, one of the most underrated JavaScript features

.toLocaleString and friends are some of the most underrated features of JavaScript. I came over them through a few different wanderings through MDN and I've used them in like every project since.

Here, I'll show you how you can use them in your own code.

.toLocaleString is for formatting

.toLocaleString is a method present on dates and numbers, which is used to format them in a locale-specific way.

new Date().toLocaleString()
// => 24/4/2022, 10:40:00 am

By default, it will use the browser's locale, but you can specify a different one with the locale parameter.

console.log(new Date().toLocaleString('en-US'))
// => 4/24/2022, 10:40:00 AM
console.log(new Date().toLocaleString('en-GB'))
// => 24/04/2022, 10:40:00
console.log(new Date().toLocaleString('ko-KR'))
// => 2022. 4. 24. 오전 10:40:49

You can further customize the output by specifying the format of the date.

console.log(new Date().toLocaleString('en-US', {
    year: 'numeric',
    weekday: 'long',
    month: 'long',
    day: 'numeric',
    hour: 'numeric',
    minute: 'numeric',
    second: 'numeric',
    hour12: false,
}))
// => Sunday, April 24, 2022 at 10:40:00

console.log(new Date().toLocaleString('en-US', {
    dateStyle: 'full',
}))
// => Sunday, April 24, 2022

console.log(new Date().toLocaleString('en-US', {
    dateStyle: 'full',
    timeStyle: 'full',
}))
// => Sunday, April 24, 2022 at 10:40:00 AM India Standard Time

console.log(new Date().toLocaleString('en-US', {
    calendar: 'indian',
}))
// => 2/4/1944 Saka, 10:40:00 AM
// I don't know what that means either

console.log(new Date().toLocaleString('en-US', {
    dayPeriod: 'long',
}))
// => in the morning

console.log(new Date().toLocaleString('en-US', {
    era: 'long',
    dayPeriod: 'long',
    weekday: 'long',
    month: 'long',
    year: 'numeric',
    day: '2-digit',
    hour: '2-digit',
    minute: '2-digit',
    second: '2-digit',
    fractionalSecondDigits: 3,
    timeZoneName: 'long',
}))
// => Sunday, April 24, 2022 Anno Domini at 10:00:00.124 in the morning India Standard Time

This totally eliminates the need of date formatting libraries like Moment.js in your code!

Numbers too!

.toLocaleString is also a method present on numbers, which is used to format them in a locale-specific way.

console.log(10000000..toLocaleString())
// => 10,000,000

As usual, you can specify a different locale with the locale parameter.

console.log(10000000..toLocaleString('ar-EG'))
// => ١٠٬٠٠٠٬٠٠٠
// Another language I know

This one also has options.

// currency
10000..toLocaleString('en-US', {style: 'currency', currency: 'USD'})
// => $10,000.00

10000..toLocaleString('en-US', {style: 'currency', currency: 'USD', currencyDisplay: 'name'})
// => 10,000.00 US dollars

(-11.29).toLocaleString('en-US', {style: 'currency', currency: 'USD', currencySign: 'accounting'})
// => ($11.29)

(-11.29).toLocaleString('en-US', {style: 'currency', currency: 'USD', currencySign: 'standard'})
// => -$11.29

// scientific
10000..toLocaleString('en-US', {notation: 'scientific'})
// => 1E4

10000..toLocaleString('en-US', {notation: 'compact'})
// => 10K
1234..toLocaleString('en-US', {notation: 'compact'})
// => 1.2K

1234..toLocaleString('en-US', {notation: 'engineering'})
// => 1.234E3

1234..toLocaleString('en-US', {notation: 'engineering', signDisplay: 'always'})
// => +1.234E3

0.55.toLocaleString('en-US', {style: 'percent'})
// => 55%

1234..toLocaleString('en-US', {style: 'unit', unit: 'liter'})
// => 1,234 L

1234..toLocaleString('en-US', {style: 'unit', unit: 'liter', unitDisplay: 'narrow'})
// => 1,234L

Once again, this removes the need for a ton of libraries for number formatting!

---

That was one of the most surprising JavaScript moments for me. Sure, I knew that JavaScript was aware of timezones, but getting access to a whole formatting library? 🤯

Comments

[JoelBonetR 🥇]

Not only in JS, there are bugs in some games due to forgetting about this when dealing with dates in C# in Unity and so on 😆

[Siddharth]

Haha, dates are a pain

[Marcel Birkenkamp]

Blain is a Pain

[JoelBonetR 🥇]

No Pain no Blain 💪🏼😂

[Eiyad Z.]

I have used it for dates before, but really didn’t realize that I can do all of this ☺️

Great Article! 👏🏻👏🏻

[Oluwapelumi Odumosu]

My mind is blown, I've used it a ton of times for date formatting but didn't even know it had some more properties for dates! And that it can also be used for numbers 🤯.
I'm definitely trying this out.
Thanks for this piece.

[busyxiang]

Didn't even realise you can do all this, thank you for the sharing

[venkatesanmca008]

good one ..

[Rishi U]

awesome, why the .. for some items and not others?

[Siddharth]

In JavaScript, you can't directly access properties on numbers. You can either use 2 dots or braces instead

10.toString() // error
(10).toString() // ok
10..toString() // ok

[Mohamed Achaq]

I'm using this feature a lot when displaying dates !

[Frodo]

Thank you.

[Thomas Bnt]

Good post and useful feature 👌

[Siddharth]

Thanks!

[Yash Desai]

Thanks for sharing 👍