Async/Await Module-based Node.js API Framework built on Koa (the successor to Express)
Last updated 2 years ago by rickyk586 .
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Async/Await Module-based Node.js API Framework built on Koa (the successor to Express)

The purpose of Velkro is to give you a structure for your API code. It allows you to chunk your code into modules, with each module having a routes definition, and optionally a controller and model. Routes are automatically pulled from modules and added to the http server. Velkro also allows you to easily add middleware across the entire API, per group of routes, or per individual routes. It is mostly unopinionated, leaving the data layer up to you. It does however handle JSON body (using koa-bodyparser), JSON Web Tokens, CORS (using @koa/cors), AJAX respond object structure, and internal/external error handling.


Velkro requires node v7.6.0 or higher for ES2015 and async function support. (required by Koa)

$ npm install velkro --save

Hello Velkro

const Velkro = require('velkro');

const app = new Velkro().on('error', e => console.error(e));
app.ready.then(() => console.log('API Ready!'));

Sample App

Check out test/sample-app for an example app.

Constructor defaults

new Velkro({
	port: '8080',
	modulesDir: 'modules',
	middlewares: [],			//added to each route
	startHttpServer: true,
	routes: {
		filename: 'routes.js',
		base: ''			//url base
	cors: {
		enabled: true,
		options: {}			//passed through to @koa/cors
	jwt: {
		secret: null

Recommended File Structure

  • middleware/
  • modules/
    • module1/
      • controller.js
      • module.js
      • routes.js
    • module2/
      • module2a/ (nested module)
        • controller.js
        • module.js
        • routes.js
      • controller.js
      • module.js
      • routes.js
  • server.js


Sample routes.js:

const controller = require('./controller');

const loginRequired = require('../../middleware/security/login-required');
const canViewSecret = require('../../middleware/security/can-view-secret');

module.exports = [
		routes: {
			post: {
					return 'test';
				'login': controller.login,
				'register': controller.register,
	}, {
		middleware: loginRequired,
		routes: {
			get: {
				'me': controller.getMe,
				'me-secret': {
					middleware: [canViewSecret],
					handler: controller.getMeSecret
			post: {
				'me': controller.updateMe

Assuming this file is in modules/user, this will create these routes:

POST /user/login POST /user/register GET /user/me GET /user/me-secret POST /user/me

As you can see, middleware can be added for a group of routes, or for one individually.


Each route in routes.js is linked to a method in the controller. The data returned by the method is the data that's sent back to the user (see AJAX response object below). Each method can optionally be async. It's good practice to put validation and filtering in controller methods. Each method is passed the ctx object from Koa.

Sample controller.js:

const model = require('./model');

module.exports = {
	async login(ctx){
	async getMe(ctx){
	//... other methods used in routes.js

Model (optional)

You can optionally have a model for each module. It's good practice to put external data-fetching here (like from a DB). It's also good practice to only allow models to call other models (instead of controllers).

Sample model.js:

const DB = require('../../libs/db');

module.exports = {
	async login(username, password){
	async getMe(id){
	//... other methods used in controller.js, or other models

AJAX Response Object

The data returned by each route is in a standardized object format:

	"actions": [],
	"errors": [{
		"msg": "",
		"handle": ""	
	"notices": [],
	"jwt": "",
	"data": {}

Data returned by each controller method is put into "data". Errors are added to the "errors" array (see Error Handling below). "actions" can be used by the frontend to perform a task as instructed by the backend. You can add an action by calling ctx.ajax.addAction('the-action'). "notices" work in a similar way (with ctx.ajax.addNotice()). Errors can be added using ctx.ajax.addError(handle, message, data).

Error Handling

Using Async/Await (promises in general) everywhere allows us to take advantage of having one exception channel. That is, if an error occurs, an exception is thrown and it flows back up through the call stack where it can be caught anywhere along the way using try/catch.

(Please see the 'test-error' route in test/sample-app/modules/routes.js to follow an example of error handling)

Velkro offers two specialized Errors to assist with error handling:


const {InternalError} = require('velkro/lib/errors');

This is to be used when an error occurs in a model. For example, if the password is found to be incorrect in modules/user/model.js:login(), then you can throw InternalError('incorrect-password'). It can also be used for errors that a user should never see.


const {ExternalError} = require('velkro/lib/errors');

This is to be used when an error is meant to be displayed to the user. To continue the example above, the InternalError can be caught and converted to an ExternalError like so:

module.exports = {
	async testError(ctx){
			await model.testError();
			if(e.handle === 'incorrect-password'){
				throw ExternalError('incorrect-password', 'The password you provided is incorrect');
				throw e;
		return 'no error';

If an InternalError makes its way all the way back up (for example, if throw e above ran because e.handle did not match), then it is added to the AJAX object errors array with the handle 'internal-error' and the message "Internal Error". ExternalErrors are added to the AJAX object errors array with the same handle and message that they were constructed with, so that they can be handled by the frontend accordingly.

JSON Web Tokens

If jwt.secret is set in the Velkro constructor, then JWT functionality is added. All you have to do is set ctx.state.user to the data that you want in the token. This will set the "jwt" value of the AJAX object. The frontend needs to then store the token (for example in a cookie) and pass it along with each request by setting the 'Authorization' header (please see the 'login-required endpoint - logged in' test in test/tests/application.js for an example). ctx.state.user is then set to the token data, which for example can be used for determining if a user is logged in or not (see test/sample-app/middleware/security/login-required.js).

(koa-jwt is used for upstream token validation/parsing, and jsonwebtoken is used for downstream token signing)


The app instance returned from new Velkro() is an event emitter that emits these events:

  • 'middleware-added' //called when all the core middleware has been added
  • 'routes-loaded' //called when all routes have been loaded
  • 'http-server-started' //called when the server has started
  • 'external-error' //called on each external error (see Error Handling)
  • 'internal-error' //called on each internal error (see Error Handling)
  • 'unknown-error' //called on each unknown error (not internal or external)
  • 'err' //called on any error (any of above)

The event is emitted with the Koa app as the first parameter. The 'routes-loaded' event is emitted with a second parameter of an object showing all of the routes like so:

    "/user": [
        "POST login",
        "GET me"
    "": [
        "GET ",
        "GET xyz"

app.ready is a promise that resolves with the Koa app when the Velkro app is completely loaded.

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