@inquirer/core

The @inquirer/core package is the library enabling the creation of Inquirer prompts.

It aims to implements a lightweight API similar to React hooks - but without JSX.

Installation

npm install @inquirer/core

yarn add @inquirer/core

Usage

import chalk from 'chalk';
import {
  createPrompt,
  useState,
  useKeypress,
  isEnterKey,
  usePrefix,
} from '@inquirer/core';

const confirm = createPrompt<boolean, { message: string; default?: boolean }>(
  (config, done) => {
    const [status, setStatus] = useState('pending');
    const [value, setValue] = useState('');
    const prefix = usePrefix({});

    useKeypress((key, rl) => {
      if (isEnterKey(key)) {
        const answer = value ? /^y(es)?/i.test(value) : config.default !== false;
        setValue(answer ? 'yes' : 'no');
        setStatus('done');
        done(answer);
      } else {
        setValue(rl.line);
      }
    });

    let formattedValue = value;
    let defaultValue = '';
    if (status === 'done') {
      formattedValue = chalk.cyan(value);
    } else {
      defaultValue = chalk.dim(config.default === false ? ' (y/N)' : ' (Y/n)');
    }

    const message = chalk.bold(config.message);
    return `${prefix} ${message}${defaultValue} ${formattedValue}`;
  },
);

/**
 *  Which then can be used like this:
 */
const answer = await confirm({ message: 'Do you want to continue?' });

See more examples:

• Confirm Prompt
• Input Prompt
• Password Prompt
• Editor Prompt
• Select Prompt
• Checkbox Prompt
• Rawlist Prompt
• Expand Prompt

API

createPrompt(viewFn)

The createPrompt function returns an asynchronous function that returns a cancelable promise resolving to the valid answer a user submit. This prompt function takes the prompt configuration as its first argument (this is defined by each prompt), and the context options as a second argument.

The prompt configuration is unique to each prompt. The context options are:

Property	Type	Required	Description
input	NodeJS.ReadableStream	no	The stdin stream (defaults to process.stdin)
output	NodeJS.WritableStream	no	The stdout stream (defaults to process.stdout)
clearPromptOnDone	boolean	no	If true, we'll clear the screen after the prompt is answered

The cancelable promise exposes a cancel method that'll exit the prompt and reject the promise.

Typescript

If using typescript, createPrompt takes 2 generic arguments (ex createPrompt<string, { message: string }>())

The first one is the type of the resolved value; function createPrompt<Value>(): Promise<Value> {}

The second one is the type of the prompt config; in other words the interface the created prompt will provide to users.

Hooks

Hooks can only be called within the prompt function and are used to handle state and events.

Those hooks are matching the React hooks API:

• useState
• useRef
• useEffect
• useMemo

And those are custom utilities from Inquirer:

• useKeypress
• usePagination
• usePrefix

Key utilities

Listening for keypress events inside an inquirer prompt is a very common pattern. To ease this, we export a few utility functions taking in the keypress event object and return a boolean:

• isEnterKey()
• isBackspaceKey()
• isSpaceKey()
• isUpKey() - Note: this utility will handle vim and emacs keybindings (up, k, and ctrl+p)
• isDownKey() - Note: this utility will handle vim and emacs keybindings (down, j, and ctrl+n)
• isNumberKey() one of 1, 2, 3, 4, 5, 6, 7, 8, 9, 0

usePagination

When looping through a long list of options (like in the select prompt), paginating the results appearing on the screen at once can be necessary. The usePagination hook is the utility used within the select and checkbox prompts to cycle through the list of options.

Pagination works by taking in the list of options and returning a subset of the rendered items that fit within the page. The hook takes in a few options. It needs a list of options (items), and a pageSize which is the number of lines to be rendered. The active index is the index of the currently selected/selectable item. The loop option is a boolean that indicates if the list should loop around when reaching the end: this is the default behavior. The pagination hook renders items only as necessary, so it takes a function that can render an item at an index, including an active state, called renderItem.

export default createPrompt((config, done) => {
  const [active, setActive] = useState(0);

  const allChoices = config.choices.map((choice) => choice.name);

  const page = usePagination({
    items: allChoices,
    active: active,
    renderItem: ({ item, index, isActive }) => `${isActive ? ">" : " "}${index}. ${item.toString()}`
    pageSize: config.pageSize,
    loop: config.loop,
  });

  return `... ${page}`;
});

Theming

Theming utilities will allow you to expose customization of the prompt style. Inquirer also has a few standard theme values shared across all the official prompts.

To allow standard customization:

import { createPrompt, usePrefix, makeTheme, type Theme } from '@inquirer/core';
import type { PartialDeep } from '@inquirer/type';

type PromptConfig = {
  theme?: PartialDeep<Theme>;
};

export default createPrompt<string, PromptConfig>((config, done) => {
  const theme = makeTheme(config.theme);

  const prefix = usePrefix({ isLoading, theme });

  return `${prefix} ${theme.style.highlight('hello')}`;
});

To setup a custom theme:

import { createPrompt, makeTheme, type Theme } from '@inquirer/core';
import type { PartialDeep } from '@inquirer/type';

type PromptTheme = {};

const promptTheme: PromptTheme = {
  icon: '!',
};

type PromptConfig = {
  theme?: PartialDeep<Theme<PromptTheme>>;
};

export default createPrompt<string, PromptConfig>((config, done) => {
  const theme = makeTheme(promptTheme, config.theme);

  const prefix = usePrefix({ isLoading, theme });

  return `${prefix} ${theme.icon}`;
});

The default theme keys cover:

type DefaultTheme = {
  prefix: string;
  spinner: {
    interval: number;
    frames: string[];
  };
  style: {
    answer: (text: string) => string;
    message: (text: string) => string;
    error: (text: string) => string;
    defaultAnswer: (text: string) => string;
    help: (text: string) => string;
    highlight: (text: string) => string;
    key: (text: string) => string;
  };
};

License

Copyright (c) 2023 Simon Boudrias (twitter: @vaxilart)
Licensed under the MIT license.