kleur

What is kleur?

The kleur npm package is a library for formatting terminal text with ANSI colors. It provides a simple and chainable API to style strings that are output to the console with various colors, backgrounds, and text styles.

What are kleur's main functionalities?

Coloring text

This feature allows you to apply text color to your console output. The example shows how to color the text green.

const kleur = require('kleur');
console.log(kleur.green('Hello world!'));

Chaining styles

Kleur supports chaining multiple styles together. In this example, the text 'Error!' is styled to be red, bold, and underlined.

const kleur = require('kleur');
console.log(kleur.red().bold().underline('Error!'));

Background colors

You can also set background colors for your text. Here, the text 'Info' has a blue background with white foreground color.

const kleur = require('kleur');
console.log(kleur.bgBlue().white('Info'));

Conditional styling

Kleur allows conditional styling, where you can enable or disable colors based on certain conditions. In this example, the red color is applied only if the environment is not production.

const kleur = require('kleur');
const enabled = process.env.NODE_ENV !== 'production';
console.log(kleur.enabled(enabled).red('Only styled if not in production'));

Other packages similar to kleur

chalk

Chalk is a popular npm package similar to kleur that allows for styling terminal strings. It offers a more extensive API and additional features like template literal support and custom themes, but it is slightly larger in size compared to kleur.

colors

Colors is another package that provides ANSI color formatting for text in the terminal. It extends String.prototype to add color properties, which some developers may find less clean than the functional approach taken by kleur.

ansi-colors

Ansi-colors is a lightweight package that focuses on performance. Like kleur, it does not extend String.prototype and has a chainable API, but it has fewer dependencies and is designed to be as minimal as possible.

README

The fastest Node.js library for formatting terminal text with ANSI colors~!

Features

• No dependencies
• Super lightweight & performant
• Supports nested & chained colors
• No String.prototype modifications
• Conditional color support
• Fully treeshakable
• Familiar API

As of v3.0 the Chalk-style syntax (magical getter) is no longer used.
Please visit History for migration paths supporting that syntax.

Install

$ npm install --save kleur

Usage

import kleur from 'kleur';

// basic usage
kleur.red('red text');

// chained methods
kleur.blue().bold().underline('howdy partner');

// nested methods
kleur.bold(`${ white().bgRed('[ERROR]') } ${ kleur.red().italic('Something happened')}`);

Chained Methods

const { bold, green } = require('kleur');

console.log(bold().red('this is a bold red message'));
console.log(bold().italic('this is a bold italicized message'));
console.log(bold().yellow().bgRed().italic('this is a bold yellow italicized message'));
console.log(green().bold().underline('this is a bold green underlined message'));

Nested Methods

const { yellow, red, cyan } = require('kleur');

console.log(yellow(`foo ${red().bold('red')} bar ${cyan('cyan')} baz`));
console.log(yellow('foo ' + red().bold('red') + ' bar ' + cyan('cyan') + ' baz'));

Conditional Support

Toggle color support as needed; kleur includes simple auto-detection which may not cover all cases.

Note: Both kleur and kleur/colors share the same detection logic.

import kleur from 'kleur';

// manually disable
kleur.enabled = false;

// or use another library to detect support
kleur.enabled = require('color-support').level > 0;

console.log(kleur.red('I will only be colored red if the terminal supports colors'));

Important:
Colors will be disabled automatically in non TTY contexts. For example, spawning another process or piping output into another process will disable colorization automatically. To force colors in your piped output, you may do so with the FORCE_COLOR=1 environment variable:

$ node app.js #=> COLORS
$ node app.js > log.txt  #=> NO COLORS
$ FORCE_COLOR=1 node app.js > log.txt #=> COLORS
$ FORCE_COLOR=0 node app.js > log.txt #=> NO COLORS

API

Any kleur method returns a String when invoked with input; otherwise chaining is expected.

It's up to the developer to pass the output to destinations like console.log, process.stdout.write, etc.

The methods below are grouped by type for legibility purposes only. They each can be chained or nested with one another.

Colors:

black — red — green — yellow — blue — magenta — cyan — white — gray — grey

Backgrounds:

bgBlack — bgRed — bgGreen — bgYellow — bgBlue — bgMagenta — bgCyan — bgWhite

Modifiers:

reset — bold — dim — italic* — underline — inverse — hidden — strikethrough*

^{* Not widely supported}

Individual Colors

When you only need a few colors, it doesn't make sense to import all of kleur because, as small as it is, kleur is not treeshakeable, and so most of its code will be doing nothing. In order to fix this, you can import from the kleur/colors submodule which fully supports tree-shaking.

The caveat with this approach is that color functions are not chainable~!
Each function receives and colorizes its input. You may combine colors, backgrounds, and modifiers by nesting function calls within other functions.

// or: import * as kleur from 'kleur/colors';
import { red, underline, bgWhite } from 'kleur/colors';

red('red text');
//~> kleur.red('red text');

underline(red('red underlined text'));
//~> kleur.underline().red('red underlined text');

bgWhite(underline(red('red underlined text w/ white background')));
//~> kleur.bgWhite().underline().red('red underlined text w/ white background');

Note: All the same colors, backgrounds, and modifiers are available.

Conditional Support

The kleur/colors submodule also allows you to toggle color support, as needed.
It includes the same initial assumptions as kleur, in an attempt to have colors enabled by default.

Unlike kleur, this setting exists as kleur.$.enabled instead of kleur.enabled:

import * as kleur from 'kleur/colors';
// or: import { $, red } from 'kleur/colors';

// manually disabled
kleur.$.enabled = false;

// or use another library to detect support
kleur.$.enabled = require('color-support').level > 0;

console.log(red('I will only be colored red if the terminal supports colors'));

Benchmarks

Using Node v10.13.0

Load time

chalk        :: 5.303ms
kleur        :: 0.488ms
kleur/colors :: 0.369ms
ansi-colors  :: 1.504ms

Performance

# All Colors
  ansi-colors      x 177,625 ops/sec ±1.47% (92 runs sampled)
  chalk            x 611,907 ops/sec ±0.20% (92 runs sampled)
  kleur            x 742,509 ops/sec ±1.47% (93 runs sampled)
  kleur/colors     x 881,742 ops/sec ±0.19% (98 runs sampled)

# Stacked colors
  ansi-colors      x  23,331 ops/sec ±1.81% (94 runs sampled)
  chalk            x 337,178 ops/sec ±0.20% (98 runs sampled)
  kleur            x  78,299 ops/sec ±1.01% (97 runs sampled)
  kleur/colors     x 104,431 ops/sec ±0.22% (97 runs sampled)

# Nested colors
  ansi-colors      x  67,181 ops/sec ±1.15% (92 runs sampled)
  chalk            x 116,361 ops/sec ±0.63% (94 runs sampled)
  kleur            x 139,514 ops/sec ±0.76% (95 runs sampled)
  kleur/colors     x 145,716 ops/sec ±0.97% (97 runs sampled)

History

This project originally forked ansi-colors.

Beginning with kleur@3.0, the Chalk-style syntax (magical getter) has been replaced with function calls per key:

// Old:
c.red.bold.underline('old');

// New:
c.red().bold().underline('new');

^{As I work more with Rust, the newer syntax feels so much better & more natural!}

If you prefer the old syntax, you may migrate to ansi-colors or newer chalk releases.
Versions below kleur@3.0 have been officially deprecated.

License

MIT © Luke Edwards