30-seconds-of-code/snippets/js/s/numeric-separator.md

title, shortTitle, type, language, tags, author, cover, excerpt, dateModified

title	shortTitle	type	language	tags	author	cover	excerpt	dateModified
JavaScript's numeric separators explained	Numeric separators explained	story	javascript	math type	chalarangelo	coffee-drip	Numeric separators are a somewhat lesser-known JavaScript syntactic sugar that can make working with large constants a lot easier.	2021-06-27T05:00:00-04:00

Numeric separators are a lesser-known JavaScript syntactic sugar that can make working with numeric constants a lot easier. The long and short of it is that you can add underscores (_) to numeric values to make them more readable.

The idea of separating large numeric values with a special character might sound familiar on account of it being a syntax present in multiple other languages, such as Java, Python, Ruby etc. From what I can tell, numeric separators are at their best when creating shared constants that will not change and are very large, have many repeated digits and/or can be ambiguous.

Apart from readability, numeric separators don't really offer anything else. For the sceptics among us that don't really see a lot of readability value either, I'd like to show two rather convincing sample cases:

// How many zeroes is that? Millions? Billions? Trillions?
const msInOneYear = 31536000000;
// Is this 4,200 or 42.00 (in cents)?
const price = 4200;

// Ok, this is approximately 31.5 billion
const msInOneYear = 31_536_000_000;
// Based on the separator, this should be 42.00 (cents)
const price = 42_00;

Finally, as far as caveats go, you only need to remember that numbers cannot start or end with a numeric separator and that you can't have two or more numeric separators in a row.