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Examplr: Node.js Example Runner

npm CircleCI

Because all packages should have an examples folder (including this one).


Examplr is a lightweight tool for adding examples to your project. Write the smallest amount of code possible to demonstrate the critical elements of your module: the configuration, the input, and the output.

Examplr handles configuration options, simple arguments, log output, and process execution. Examples can be async functions or return promises. Errors and rejections are handled and logged correctly.

Here's what an example for getting a user with an API client might look like

import createClient from '../lib'

export default ({apiKey, reqId, log}) => async (userId = 'user-id') => {
  const client = createClient({apiKey, reqId, log})
  const { name } = await client.getUserById(userId)
  return name

Run with Examplr, some convenient magic happens: the API key is automatically passed in as an option, either from the environment variable API_KEY or from a local JSON file (ignored by version control); the user id can be passed in as an argument from the command line; a Pino logger is created with colorized formatting; and the user name is fetched asynchronously and logged.

Try it out

Clone this and run the included example, then copy the examples folder into your own project to get started.

$ git clone
$ cd node-examplr
$ yarn
$ yarn example adventure
$ yarn example adventure Jake 28



Add this as a development dependency to your project using npm with

$ npm install --dev @meltwater/examplr

or using Yarn with

$ yarn add --save-dev @meltwater/examplr


Refer to the examples folder for working examples and additional instructions you can copy directly into your project.

Getting started

Create an entry point for examples,

/* examples/index.js */

import path from 'path'

import { createExamples } from '@meltwater/examplr'

// Normally examples are imported from other files:
// add this one here for demonstration.
const adventureTime = ({
}) => (me = 'Finn') => {{friends}, 'Ready')
  return `${me}, Jake, and ${friends}.`

const { runExample } = createExamples({
  examples: {adventureTime},
  defaultOptions: {
    logLevel: 'info',
    logOutputMode: 'short',
    friends: 'Lumpy Space Princess'

  local: path.resolve('examples', 'local.json')

This can now be run with custom arguments with

$ node ./examples adventure-time Snail

Add any of the following to your project's npm scripts to enable running with npm run example or yarn run example, etc.,

  "scripts": {
    "example": "node examples",
    "example:watch": "nodemon examples",
    "example:inspect": "node --inspect examples",
    "example:inspect:watch": "nodemon --inspect examples",

Example functions

  • Examples are higher order functions which take an options object and return either a synchronous function, an async function, or a function which returns a promise.
  • The returned function will be called with any command line arguments.
  • The return value or resolution value will be logged under data.
  • If an error is thrown or the promise is rejected, the error will be logged under err.
  • The process will exit after the function returns or throws, or the promise resolves or rejects.
    • To use callback style modules wrap them in a promise.
    • To run background processes, return a promise that does not resolve.

Example options

All examples are passed a single argument containing the logger and all options. This argument will always at least contain the logger as the log property.

  • Available options are defined by listing the corresponding environment variables in envVars.
  • Each environment variable name will be converted to camelcase and added with its value to the options object.
  • The optional local option in runExample points to a JSON file to read and merge with the options (if this file exists).
  • The defaultOptions are used to set default values for any undefined options.
  • The option priority follows: environment variables override local JSON values override defaults.


The logger is a Pino logger.

  • Any custom serializers are used in addition to the standard serializers.
  • Each filter in logFilters should be a function that takes the JSON log document and returns true if the log should be printed and false otherwise.
  • The options LOG_LEVEL, LOG_OUTPUT_MODE and LOG_FILTER are built in, but must be enabled by adding them to the envVars array.
  • The logLevel may be any supported Pino level.
  • The logFilter is a property name in logFilters (no filter by default).
  • The logOutputMode may be either json (unformatted), pretty (the Pino pretty formatter), or any mode supported by bunyan-formatter: short (default), long, simple, or bunyan.

API Reference

createExamples({examples, envVars, defaultOptions, createLogger})

Takes a single options argument with the following parameters and returns the object {runExample}. All options are optional.

  • examples: Object of examples to register.
  • envVars: Array of environment variables to read into options.
  • defaultOptions: Object of default options to pass to examples.
  • logSerializers: Log serializers to pass to createLogger.
  • logFilters: Object of named log filters (available via logFilter).
  • createLogger: Custom function to use for creating the logger.


Run the example with the provided command line arguments. Gets the name of the example to run as the first CLI argument and passes the rest to the example. If no example is given, lists available examples.

The optional local option is the path to a config file to read for example options (if it exists).

getPinoArgs({outputMode, outputFilter, serializers, ...options})

Only use this method in development.

This is a convenience method for users of this package who use Pino in development outside of their examples and want logging output formatted consistently.

The Pino output stream will be directed though the selected formatter, thus logs will be pretty-printed without needing to pipe them though the Pino CLI.

Returns the arguments (as an array) that are passed to the pino instantiation function, e.g.,

import pino from 'pino'

import { getPinoArgs } from '@meltwater/examplr'

const args = getPinoArgs({
  outputMode: 'short',
  outputFilter: log => === 'bar',
  serializers: {foo: x => x.toLowerCase()},
  // addtional options are passed to pino

const log = pino(...args)

Development Quickstart

$ git clone
$ cd node-examplr
$ nvm install
$ yarn

Run each command below in a separate terminal window:

$ yarn run watch
$ yarn run test:watch

Development and Testing

Source code

The node-examplr source is hosted on GitHub. Clone the project with

$ git clone


You will need Node.js with npm, Yarn, and a Node.js debugging client.

Be sure that all commands run under the correct Node version, e.g., if using nvm, install the correct version with

$ nvm install

Set the active version for each shell session with

$ nvm use

Install the development dependencies with

$ yarn


CircleCI should already be configured: this section is for reference only.

The following environment variables must be set on CircleCI:

  • NPM_TOKEN: npm token for installing and publishing packages.
  • NPM_TEAM: npm team to grant read-only package access (format org:team, optional).

These may be set manually or by running the script ./.circleci/

Development tasks

Primary development tasks are defined under scripts in package.json and available via yarn run. View them with

$ yarn run

Production build

Lint, test, and transpile the production build to dist with

$ yarn run dist
Publishing a new release

Release a new version using npm version. This will run all tests, update the version number, create and push a tagged commit, and trigger CircleCI to publish the new version to npm.

  • Update the CHANGELOG before each new release after version 1.
  • New versions are released when the commit message is a valid version number.
  • Versions are only published on release branches: master branch or any branch matching ver/*.
  • If branch protection options are enabled, you must first run npm version on a separate branch, wait for the commit to pass any required checks, then merge and push the changes to a release branch.
  • Do not use the GitHub pull request button to merge version commits as the commit tagged with the new version number will not match after merging.


See the full documentation on using examples.

View all examples with

$ yarn run example


Linting against the JavaScript Standard Style and JSON Lint is handled by gulp.

View available commands with

$ yarn run gulp --tasks

Run all linters with

$ yarn run lint

In a separate window, use gulp to watch for changes and lint JavaScript and JSON files with

$ yarn run watch

Automatically fix most JavaScript formatting errors with

$ yarn run format


Unit and integration testing is handled by AVA and coverage is reported by Istanbul.

  • Test files end in .spec.js.
  • Unit tests are placed under lib alongside the tested module.
  • Integration tests are placed in test.
  • Static files used in tests are placed in fixtures.

Watch and run tests on changes with

$ yarn run test:watch

If using AVA snapshot testing, update snapshots with

$ yarn run test:update

Generate a coverage report with

$ yarn run report

An HTML version will be saved in coverage.

Debugging tests

Create a breakpoint by adding the statement debugger to the test and start a debug session with, e.g.,

$ yarn run test:inspect lib/examples.spec.js

Watch and restart the debugging session on changes with

$ yarn run test:inspect:watch lib/examples.spec.js


The author and active contributors may be found in package.json,

$ jq .author < package.json
$ jq .contributors < package.json

To submit a patch:

  1. Request repository access by submitting a new issue.
  2. Create your feature branch (git checkout -b my-new-feature).
  3. Make changes and write tests.
  4. Commit your changes (git commit -am 'Add some feature').
  5. Push to the branch (git push origin my-new-feature).
  6. Create a new Pull Request.


This npm package is licensed under the MIT license.


This software is provided by the copyright holders and contributors "as is" and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. In no event shall the copyright holder or contributors be liable for any direct, indirect, incidental, special, exemplary, or consequential damages (including, but not limited to, procurement of substitute goods or services; loss of use, data, or profits; or business interruption) however caused and on any theory of liability, whether in contract, strict liability, or tort (including negligence or otherwise) arising in any way out of the use of this software, even if advised of the possibility of such damage.