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Number Format CLI with Intl

A Node CLI that formats a number for a given locale, supporting grouping, compact notation, and currency display via the Intl API.

node --version

node numfmt.mjs 1234567.891 en-US currency USD

node --test numfmt.test.mjs

Prints the number formatted per locale and options, for example $1,234,567.89 for US currency.

What it does

Builds an Intl.NumberFormat from the locale and style arguments, choosing the right option set for plain, currency, compact, or percent output, and validates that the input is a finite number.

const [valueArg, locale = 'en-US', style = 'decimal', currency] = process.argv.slice(2);
const value = Number(valueArg);
if (!Number.isFinite(value)) { console.error('usage: numfmt <number> [locale] [decimal|currency|compact|percent] [code]'); process.exit(1); }

const options = { decimal: {}, currency: { style: 'currency', currency: currency ?? 'USD' }, compact: { notation: 'compact' }, percent: { style: 'percent' } }[style];
if (!options) { console.error('unknown style: ' + style); process.exit(1); }
console.log(new Intl.NumberFormat(locale, options).format(value));

Run and verify

node numfmt.mjs 1234567.891 en-US currency USD

Run the test command to check the implementation: node --test numfmt.test.mjs.

Expected Output

Formatting 1234567.891 as US currency rounds to cents and groups thousands:

$1,234,567.89

Limitations

Output depends on the ICU data bundled with the Node build; a small-icu build may fall back to a simplified locale, which changes the formatting.