JavaScript library to generate a human readable String describing the file size
The filesize npm package is a library designed to provide simple file size conversion and formatting. It allows users to convert raw file size numbers into human-readable strings, with support for multiple units and customization options. This can be particularly useful in applications where file sizes need to be displayed to users in a format that is easy to understand.
Basic file size formatting
Converts a file size in bytes to a human-readable string using the most appropriate unit. In this example, 1024 bytes are converted to '1 KB'.
"const filesize = require('filesize');
console.log(filesize(1024)); // '1 KB'"Customizing the output
Allows customization of the output format, including rounding and the spacer between the number and the unit. This example shows no rounding and removes the space between the number and the unit.
"const filesize = require('filesize');
console.log(filesize(1024, {round: 0, spacer: ''})); // '1KB'"Using different units
Supports using different unit standards, such as the International Electrotechnical Commission (IEC) standard, which uses 'KiB' instead of 'KB' for 1024 bytes.
"const filesize = require('filesize');
console.log(filesize(1024, {standard: 'iec'})); // '1 KiB'"Similar to filesize, pretty-bytes converts byte values into a human-readable format. It focuses on simplicity and does not offer as many customization options as filesize, making it a good choice for straightforward use cases.
The bytes package also provides functionality for formatting byte sizes into human-readable strings. It offers a balance between simplicity and customization, with options to specify the number of decimal places and the units to use.
A lightweight, high-performance file size utility for JavaScript that converts bytes to human-readable strings. Works in both Node.js and browser environments with comprehensive format support.
npm install filesize
import {filesize} from "filesize";
filesize(265318, {standard: "jedec"}); // "259.1 KB"
const {filesize} = require("filesize");
filesize(1024); // "1.02 kB"
import {partial} from "filesize";
const size = partial({standard: "jedec"});
size(265318); // "259.1 KB"
{Number|String|BigInt} - The value to convert (required){Object} - Configuration object (optional){Number} - Number base, default is 10{Boolean} - Enables bit sizes, default is false{Number} - Specifies the symbol via exponent, e.g. 2 is MB for base 2, default is -1{Boolean} - Enables full form of unit of measure, default is false{Array} - Array of full form overrides, default is []{String|Boolean} - BCP 47 language tag to specify a locale, or true to use default locale, default is ""{Object} - Dictionary of options defined by ECMA-402 (Number.prototype.toLocaleString){String} - Output of function (array, exponent, object, or string), default is string{Boolean} - Decimal place end padding, default is false{Number} - Sets precision of numerical output, default is 0{Number} - Decimal place, default is 2{String} - Rounding method, can be round, floor, or ceil, default is round{String} - Decimal separator character, default is an empty string{String} - Character between the result and symbol, default is " "{String} - Standard unit of measure, can be iec, jedec, or si. Default is si (base 10){Object} - Dictionary of IEC/JEDEC symbols to replace for localizationThe function validates input and throws TypeError for invalid values:
// Invalid input will throw TypeError
try {
filesize("invalid");
} catch (error) {
console.error(error.message); // "Invalid input"
}
try {
filesize(NaN);
} catch (error) {
console.error(error.message); // "Invalid input"
}
filesize.js maintains 100% test coverage across all metrics with a comprehensive test suite of 47 test cases:
-------------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
-------------|---------|----------|---------|---------|-------------------
All files | 100 | 100 | 100 | 100 |
filesize.js | 100 | 100 | 100 | 100 |
-------------|---------|----------|---------|---------|-------------------
# Run all tests (linting + unit tests)
npm test
# Run only unit tests
npm run mocha
The test suite comprehensively covers:
filesize.js is optimized for high performance with comprehensive benchmarks covering various usage patterns:
| Scenario | Operations/sec | Notes |
|---|---|---|
| Basic conversion | ~8-19M ops/sec | Fastest operations (small numbers) |
| Large numbers | ~8-15M ops/sec | Consistent performance |
| With options | ~2-8M ops/sec | Depends on option complexity |
| Locale formatting | ~85K ops/sec | Most expensive operation |
| Partial functions | ~6-8M ops/sec | ~10-20% overhead, amortized |
Excellent Performance (>1M ops/sec)
Good Performance (100K-1M ops/sec)
Use Sparingly (<100K ops/sec)
# Run all benchmarks
cd benchmarks && node index.js
# Run specific benchmark
node benchmarks/basic-performance.js
# With garbage collection (more accurate)
node --expose-gc benchmarks/index.js
Benchmarks run on macOS ARM64, Node.js v23.10.0, 12 CPU cores, 24GB RAM
Converts a numeric value to a human-readable file size string.
Parameters:
input {Number|String|BigInt} - The value to convertoptions {Object} - Configuration options (optional)Returns: {String|Array|Object|Number} - Formatted size based on output option
filesize(500); // "500 B"
filesize(1024, {base: 2}); // "1 KiB"
filesize(265318, {output: "array"}); // [265.32, "kB"]
See also: partial()
Creates a pre-configured filesize function with options applied.
Parameters:
options {Object} - Configuration options to applyReturns: {Function} - New function with options pre-applied
const formatBinary = partial({base: 2, standard: "iec"});
formatBinary(1048576); // "1 MiB"
const formatBits = partial({bits: true});
formatBits(1024); // "8.19 kbit"
See also: filesize()
filesize(265318); // "265.32 kB"
filesize(265318, {separator: ","}); // "265,32 kB"
filesize(265318, {output: "array"}); // [265.32, "kB"]
filesize(1024, {output: "array", base: 2}); // [1, "KiB"]
filesize(265318, {output: "object"});
// {value: 265.32, symbol: "kB", exponent: 1, unit: "kB"}
filesize(1024, {output: "exponent"}); // 1
filesize(1048576, {output: "exponent", base: 2}); // 2
filesize(1000); // "1 kB" (base 10)
filesize(1000000); // "1 MB"
filesize(1024, {standard: "iec", base: 2}); // "1 KiB"
filesize(1048576, {standard: "iec", base: 2}); // "1 MiB"
filesize(1024, {standard: "jedec"}); // "1 KB"
filesize(1048576, {standard: "jedec"}); // "1 MB"
import {filesize} from "filesize";
filesize(500); // "500 B"
filesize(1024); // "1.02 kB"
filesize(265318); // "265.32 kB"
filesize(265318, {round: 0}); // "265 kB"
// IEC binary prefixes (KiB, MiB, GiB)
filesize(1024, {base: 2, standard: "iec"}); // "1 KiB"
filesize(1048576, {base: 2, standard: "iec"}); // "1 MiB"
// JEDEC binary format (KB, MB, GB with binary calculation)
filesize(1024, {standard: "jedec"}); // "1 KB"
filesize(265318, {standard: "jedec"}); // "259.1 KB"
filesize(500, {bits: true}); // "4 kbit"
filesize(1024, {bits: true}); // "8.19 kbit"
filesize(1024, {bits: true, base: 2}); // "8 kibit"
// Full form units
filesize(1024, {fullform: true}); // "1.02 kilobytes"
filesize(1024, {base: 2, fullform: true}); // "1 kibibytes"
// Custom separators and spacing
filesize(265318, {separator: ","}); // "265,32 kB"
filesize(265318, {spacer: ""}); // "265.32kB"
// Precision and padding
filesize(1536, {round: 3, pad: true}); // "1.536 kB"
filesize(1536, {precision: 3}); // "1.54 kB"
// German locale
filesize(265318, {locale: "de"}); // "265,32 kB"
// Custom symbols
filesize(1, {symbols: {B: "Π"}}); // "1 Π"
// Custom full forms
filesize(12, {fullform: true, fullforms: ["Π±Π°ΠΉΡΠΎΠ²"]}); // "12 Π±Π°ΠΉΡΠΎΠ²"
// Specific exponent
filesize(1024, {exponent: 0}); // "1024 B"
filesize(1024, {exponent: 1}); // "1.02 kB"
// BigInt support
filesize(BigInt(1024), {standard: "jedec"}); // "1 KB"
// Extreme precision for very large numbers
filesize(Math.pow(1024, 8), {precision: 3}); // "1208925819614629174706176 YB"
import {partial} from "filesize";
// Create specialized formatters
const formatBinary = partial({base: 2, standard: "iec"});
const formatBits = partial({bits: true});
const formatPrecise = partial({round: 3, pad: true});
const formatGerman = partial({locale: "de"});
// Use throughout application
formatBinary(1048576); // "1 MiB"
formatBits(1024); // "8.19 kbit"
formatPrecise(1536); // "1.536 kB"
formatGerman(265318); // "265,32 kB"
// Method chaining equivalent
const sizes = [1024, 2048, 4096];
sizes.map(formatBinary); // ["1 KiB", "2 KiB", "4 KiB"]
This project follows Node.js best practices and uses:
filesize.js/
βββ src/
β βββ filesize.js # Main implementation
β βββ constants.js # Unit definitions and constants
βββ tests/
β βββ unit/
β βββ filesize.test.js # Comprehensive test suite
βββ types/
β βββ filesize.d.ts # TypeScript definitions
β βββ constants.d.ts # Constants type definitions
βββ package.json # Dependencies and scripts
git checkout -b feature/amazing-feature)npm test)git commit -m 'Add amazing feature')git push origin feature/amazing-feature)# Install dependencies
npm install
# Run linting
npm run lint
# Run tests
npm test
# Build distribution
npm run build
# Run all checks (lint + test)
npm run ci
Copyright (c) 2025 Jason Mulligan
Licensed under the BSD-3 license.
FAQs
JavaScript library to generate a human readable String describing the file size
The npm package filesize receives a total of 10,249,506 weekly downloads. As such, filesize popularity was classified as popular.
We found that filesize demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago.Β It has 1 open source maintainer collaborating on the project.
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