listr

Terminal task list

Install

$ npm install --save listr

Usage

const execa = require('execa');
const Listr = require('listr');

const tasks = new Listr([
	{
		title: 'Git',
		task: () => {
			return new Listr([
				{
					title: 'Checking git status',
					task: () => execa.stdout('git', ['status', '--porcelain']).then(result => {
						if (result !== '') {
							throw new Error('Unclean working tree. Commit or stash changes first.');
						}
					})
				},
				{
					title: 'Checking remote history',
					task: () => execa.stdout('git', ['rev-list', '--count', '--left-only', '@{u}...HEAD']).then(result => {
						if (result !== '0') {
							throw new Error('Remote history differ. Please pull changes.');
						}
					})
				}
			], {concurrent: true});
		}
	},
	{
		title: 'Install package dependencies',
		task: () => execa('npm', ['install'])
	},
	{
		title: 'Run tests',
		task: () => execa('npm', ['test'])
	},
	{
		title: 'Publish package',
		task: () => execa('npm', ['publish'])
	}
]);

tasks.run().catch(err => {
	console.error(err);
});

Task

A task can return different values. If a task returns, it means the task was completed successfully. If a task throws an error, the task failed.

const tasks = new Listr([
	{
		title: 'Success',
		task: () => 'Foo'
	},
	{
		title: 'Failure',
		task: () => {
			throw new Error('Bar')
		}
	}
]);

Promises

A task can also be async by returning a Promise. If the promise resolves, the task completed successfully, it it rejects, the task failed.

const tasks = new Listr([
	{
		title: 'Success',
		task: () => Promise.resolve('Foo')
	},
	{
		title: 'Failure',
		task: () => Promise.reject('Bar')
	}
]);

Observable

A task can also return an Observable. The thing about observables is that it can emit multiple values and can be used to show the output of the task. Please note that only the last line of the output is rendered.

const tasks = new Listr([
	{
		title: 'Success',
		task: () => {
			return new Observable(observer => {
				observer.next('Foo');

				setTimeout(() => {
					observer.next('Bar');
				}, 2000);

				setTimeout(() => {
					observer.complete();
				}, 4000);
			});
		}
	},
	{
		title: 'Failure',
		task: () => Promise.reject(new Error('Bar'))
	}
]);

Streams

It's also possible to return a stream. The stream will be converted to an Observable and handled as such.

Skipping tasks

Optionally specify a skip function to determine whether a task can be skipped.

• If the skip function returns a truthy value or a Promise that resolves to a truthy value then the task will be skipped.
• If the returned value is a string it will be displayed as the reason for skipping the task.
• If the skip function returns a falsey value or a Promise that resolves to a falsey value then the task will be executed as normal.
• If the skip function throws or returns a Promise that rejects, the task (and the whole build) will fail.

const tasks = new Listr([
	{
		title: 'Task 1',
		task: () => Promise.resolve('Foo')
	},
	{
		title: 'Can be skipped',
		skip: () => {
			if (Math.random() > 0.5) {
				return 'Reason for skipping';
			}
		},
		task: () => 'Bar'
	},
	{
		title: 'Task 3',
		task: () => Promise.resolve('Bar')
	}
]);

Context

A context object is being passed as argument into every skip and task function. This allows you to create composable tasks and change the behaviour of your task depending on previous results.

const tasks = new Listr([
	{
		title: 'Task 1',
		skip: ctx => ctx.foo === 'bar',
		task: () => Promise.resolve('Foo')
	},
	{
		title: 'Can be skipped',
		skip: () => {
			if (Math.random() > 0.5) {
				return 'Reason for skipping';
			}
		},
		task: ctx => {
			ctx.unicorn = 'rainbow';
		}
	},
	{
		title: 'Task 3',
		task: ctx => Promise.resolve(`${ctx.foo} ${ctx.bar}`)
	}
]);

tasks.run({
	foo: 'bar'
}).then(ctx => {
	console.log(ctx);
	//=> {foo: 'bar', unicorn: 'rainbow'}
});

Custom renderers

It's possible to write custom renderers for Listr. A renderer is an ES6 class that accepts the tasks that it should renderer, and the Listr options object. It has two methods, the render method which is called when it should start rendering, and the end method. The end method is called all the tasks are completed or if a task failed. If a task failed, the error object is passed in via an argument.

class CustomRenderer {

	constructor(tasks, options) { }

	static get nonTTY() {
		return false;
	}

	render() { }

	end(err) { }
}

module.exports = CustomRenderer;

Note: A renderer is not passed through to the subtasks, only to the main task. It is up to you to handle that case.

The nonTTY property returns a boolean indicating if the renderer supports non-TTY environments. The default for this property is false if you do not implement it.

Observables

Every task is an observable. The task emits three different events and every event is an object with a type property.

1. The state of the task has changed (STATE).
2. The task outputted data (DATA).
3. The task returns a subtask list (SUBTASKS).

This allows you to flexibly build up your UI. Let's render every task that starts executing.

class CustomRenderer {

	constructor(tasks, options) {
		this._tasks = tasks;
		this._options = Object.assign({}, options);
	}

	static get nonTTY() {
		return true;
	}

	render() {
		for (const task of this._tasks) {
			task.subscribe(event => {
				if (event.type === 'STATE' && task.isPending()) {
					console.log(`${task.title} [started]`);
				}
			});
		}
	}

	end(err) { }
}

module.exports = CustomRenderer;

If you want more complex examples, take a look at the update and verbose renderers.

API

Listr([tasks], [options])

tasks

Type: object[]

List of tasks.

title

Type: string

Title of the task.

task

Type: Function

Task function.

skip

Type: Function

Skip function. Read more about skipping tasks.

options

Any renderer specific options.

concurrent

Type: boolean
Default: false

Set to true if you want tasks to run concurrently.

renderer

Type: string object
Default: default
Options: default verbose silent

Renderer that should be used. You can either pass in the name of the known renderer, or a class of a custom renderer.

nonTTYRenderer

Type: string object
Default: verbose

The renderer that should be used if the main renderer does not support TTY environments. You can either pass in the name of the renderer, or a class of a custom renderer.

Instance

add(task)

Returns the instance.

task

Type: object object[]

Task object or multiple task objects.

run([context])

Start executing the tasks. Returns a Promise for the context object.

context

Type: object
Default: Object.create(null)

Initial context object.

Related

• ora - Elegant terminal spinner
• cli-spinners - Spinners for use in the terminal

License

MIT © Sam Verschueren