Add ability to control number of fractional digits (#62)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

index.d.ts

@@ -51,6 +51,47 @@ declare namespace prettyBytes {
 		```
 		*/
 		readonly binary?: boolean;
+
+		/**
+		The minimum number of fraction digits to display.
+
+		If neither `minimumFractionDigits` or `maximumFractionDigits` are set, the default behavior is to round to 3 significant digits.
+
+		@default undefined
+
+		```
+		import prettyBytes = require('pretty-bytes');
+
+		// Show the number with at least 3 fractional digits
+		prettyBytes(1900, {minimumFractionDigits: 3});
+		//=> '1.900 kB'
+
+		prettyBytes(1900);
+		//=> '1.9 kB'
+		```
+		*/
+		readonly minimumFractionDigits?: number;
+
+
+		/**
+		The maximum number of fraction digits to display.
+
+		If neither `minimumFractionDigits` or `maximumFractionDigits` are set, the default behavior is to round to 3 significant digits.
+
+		@default undefined
+
+		```
+		import prettyBytes = require('pretty-bytes');
+
+		// Show the number with at most 1 fractional digit
+		prettyBytes(1920, {maximumFractionDigits: 1});
+		//=> '1.9 kB'
+
+		prettyBytes(1920);
+		//=> '1.92 kB'
+		```
+		*/
+		readonly maximumFractionDigits?: number;
 	}
 }
 

index.js

@@ -54,12 +54,12 @@ Formats the given number using `Number#toLocaleString`.
 - If locale is true, the system default locale is used for translation.
 - If no value for locale is specified, the number is returned unmodified.
 */
-const toLocaleString = (number, locale) => {
+const toLocaleString = (number, locale, options) => {
 	let result = number;
 	if (typeof locale === 'string' || Array.isArray(locale)) {
-		result = number.toLocaleString(locale);
-	} else if (locale === true) {
-		result = number.toLocaleString();
+		result = number.toLocaleString(locale, options);
+	} else if (locale === true || options !== undefined) {
+		result = number.toLocaleString(undefined, options);
 	}
 
 	return result;
@@ -87,15 +87,30 @@ module.exports = (number, options) => {
 		number = -number;
 	}
 
+	let localeOptions;
+
+	if (options.minimumFractionDigits !== undefined) {
+		localeOptions = {minimumFractionDigits: options.minimumFractionDigits};
+	}
+
+	if (options.maximumFractionDigits !== undefined) {
+		localeOptions = Object.assign({maximumFractionDigits: options.maximumFractionDigits}, localeOptions);
+	}
+
 	if (number < 1) {
-		const numberString = toLocaleString(number, options.locale);
+		const numberString = toLocaleString(number, options.locale, localeOptions);
 		return prefix + numberString + ' ' + UNITS[0];
 	}
 
 	const exponent = Math.min(Math.floor(options.binary ? Math.log(number) / Math.log(1024) : Math.log10(number) / 3), UNITS.length - 1);
 	// eslint-disable-next-line unicorn/prefer-exponentiation-operator
-	number = Number((number / Math.pow(options.binary ? 1024 : 1000, exponent)).toPrecision(3));
-	const numberString = toLocaleString(number, options.locale);
+	number /= Math.pow(options.binary ? 1024 : 1000, exponent);
+
+	if (!localeOptions) {
+		number = number.toPrecision(3);
+	}
+
+	const numberString = toLocaleString(Number(number), options.locale, localeOptions);
 
 	const unit = UNITS[exponent];
 

readme.md

@@ -85,6 +85,46 @@ Default: `false` *(No localization)*
 
 **Note:** Localization should generally work in browsers. Node.js needs to be [built](https://github.com/nodejs/node/wiki/Intl) with `full-icu` or `system-icu`. Alternatively, the [`full-icu`](https://github.com/unicode-org/full-icu-npm) module can be used to provide support at runtime. [Node.js 13](https://nodejs.org/en/blog/release/v13.0.0/) and later ships with ICU by default.
 
+##### minimumFractionDigits
+
+Type: `number`\
+Default: `undefined`
+
+The minimum number of fraction digits to display.
+
+If neither `minimumFractionDigits` or `maximumFractionDigits` are set, the default behavior is to round to 3 significant digits.
+
+```js
+const prettyBytes = require('pretty-bytes');
+
+// Show the number with at least 3 fractional digits
+prettyBytes(1900, {minimumFractionDigits: 3});
+//=> '1.900 kB'
+
+prettyBytes(1900);
+//=> '1.9 kB'
+```
+
+##### maximumFractionDigits
+
+Type: `number`\
+Default: `undefined`
+
+The maximum number of fraction digits to display.
+
+If neither `minimumFractionDigits` or `maximumFractionDigits` are set, the default behavior is to round to 3 significant digits.
+
+```js
+const prettyBytes = require('pretty-bytes');
+
+// Show the number with at most 1 fractional digit
+prettyBytes(1920, {maximumFractionDigits: 1});
+//=> '1.9 kB'
+
+prettyBytes(1920);
+//=> '1.92 kB'
+```
+
 ## Related
 
 - [pretty-bytes-cli](https://github.com/sindresorhus/pretty-bytes-cli) - CLI for this module

test.js

@@ -113,3 +113,19 @@ test('bits and binary option', t => {
 	t.is(prettyBytes(1025, {bits: true, binary: true}), '1 kibit');
 	t.is(prettyBytes(1e6, {bits: true, binary: true}), '977 kibit');
 });
+
+test('fractional digits options', t => {
+	t.is(prettyBytes(1900, {maximumFractionDigits: 1}), '1.9 kB');
+	t.is(prettyBytes(1900, {minimumFractionDigits: 3}), '1.900 kB');
+	t.is(prettyBytes(1911, {maximumFractionDigits: 1}), '1.9 kB');
+	t.is(prettyBytes(1111, {maximumFractionDigits: 2}), '1.11 kB');
+	t.is(prettyBytes(1019, {maximumFractionDigits: 3}), '1.019 kB');
+	t.is(prettyBytes(1001, {maximumFractionDigits: 3}), '1.001 kB');
+	t.is(prettyBytes(1000, {minimumFractionDigits: 1, maximumFractionDigits: 3}), '1.0 kB');
+	t.is(prettyBytes(3942, {minimumFractionDigits: 1, maximumFractionDigits: 2}), '3.94 kB');
+	t.is(prettyBytes(4001, {maximumFractionDigits: 3, binary: true}), '3.907 kiB');
+	t.is(prettyBytes(18717, {maximumFractionDigits: 2, binary: true}), '18.28 kiB');
+	t.is(prettyBytes(18717, {maximumFractionDigits: 4, binary: true}), '18.2783 kiB');
+	t.is(prettyBytes(32768, {minimumFractionDigits: 2, maximumFractionDigits: 3, binary: true}), '32.00 kiB');
+	t.is(prettyBytes(65536, {minimumFractionDigits: 1, maximumFractionDigits: 3, binary: true}), '64.0 kiB');
+});