ansi-fragments

A tiny library with builders to help making logs/CLI pretty with a nice DX.

• ansi-fragments
  • Installation
  • Usage
  • API
    • color
    • modifier
    • container
    • pad
    • fixed
    • ifElse
    • provide

Installation

yarn add ansi-fragments

Usage

import { color, modifier, pad, container } from 'ansi-fragments';

const prettyLog = (level, message) => container(
  color('green', modifier('italic', level)),
  pad(1),
  message
).build();

console.log(prettyLog('success', 'Yay!'));

API

Each fragment implements IFragment interface:

interface IFragment {
  build(): string;
}

The build method is responsible for traversing the tree of fragments and create a string representation with ANSI escape codes.

color

color(
  ansiColor: AnsiColor,
  ...children: Array<string | IFragment>
): IFragment

Creates fragment for standard ANSI colors.

color('red', 'Oh no');
color('bgBlue', color('brightBlue', 'Hey'));
color('green', modifier('bold', 'Sup!'));

modifier

modifier(
  ansiModifier: AnsiModifier,
  ...children: Array<string | IFragment>
): IFragment

Creates fragment for standard ANSI modifiers: dim, bold, hidden, italic, underline, strikethrough.

modifier('underline', 'Hello', 'World');
modifier('italic', modifier('bold', 'Hey'));
modifier('bold', color('green', 'Sup!'));

container

container(...children: Array<string | IFragment>): IFragment

Creates fragment, which sole purpose is to hold and build nested fragments.

container(
  color('gray', '[08/01/18 12:00]'),
  pad(1),
  color('green', 'success'),
  pad(1),
  'Some message'
)

pad

pad(count: number, separator?: string): IFragment

Creates fragment, which repeats given separator (default: ) given number of times.

pad(1);
pad(2, '#')
pad(1, '\n')

fixed

fixed(
  value: number,
  bias: 'start' | 'end',
  ...children: Array<string | IFragment>
): IFragment

Creates fragment, which makes sure the children will always build to given number of non-ANSI characters. It will either trim the results or add necessary amount of spaces. The bias control if trimming/padding should be done at the start of the string representing built children or at the end.

fixed(5, 'start', 'ERR'); // => '  ERR'
fixed(8, 'end', color('green', 'success')); // equals to color('green', 'success') + ' '
fixed(10, 'end', 'Hello', pad(2), 'World') // => 'Hello  Wor'

ifElse

ifElse(
  condition: Condition,
  ifTrueFragment: string | IFragment,
  elseFragment: string | IFragment
): IFragment

type ConditionValue = boolean | string | number | null | undefined;
type Condition = ConditionValue | (() => ConditionValue);

Change the output based on condition. Condition can ba a primitive value, which can be casted to boolean or a function. If conation or return value of condition is evaluated to true, the first argument - ifTrueFragment will be used, otherwise elseFragment.

let condition = getConditionValue()
ifElse(
  () => condition,
  color('red', 'ERROR'),
  color('yellow', 'WARNING')
)

provide

provide<T>(
  value: T,
  builder: (value: T) => string | IFragment
): IFragment

Provides given value to a builder function, which should return string or fragment. Useful in situations when the output is connected with some calculated value - using provide you only need to calculate final value once and forward it to custom styling logic.

provide(getMessageFromSomewhere(), value => {
  switch (value.level) {
    case 'error':
      return container(
        color('red', modifier('bold', value.level.toUpperCase())),
        pad(2),
        value.log
      );
    case 'info':
      return container(
        color('blue', value.level.toUpperCase()),
        pad(2),
        value.log
      );
    default:
      return container(value.level.toUpperCase(), pad(2), value.log);
  }
})