How to Build Node.js Application with Bazel

16 minute read     Updated:

Rose Chege %
Rose Chege

This article examines how Bazel and Node.js combine for better build automation. Earthly simplifies this approach with robust caching. Learn more about Earthly.

Bazel is an open-source build tool to speed up your builds and tests. Bazel is generally used on very large projects to scale the organization’s codebase. Bazel is a multilingual build system. This guide will help you run and build Bazel with Node.js apps. We will create a Bazel workspace from scratch to build and test Node.js code.


To follow along with this article, it is helpful to have the following:

  • Basic knowledge of working with JavaScript.
  • Node.js installed on your computer.
  • Bazel installed on your computer.

Setting Up the Bazel Environment


Open your code editor in your preferred working directory. Create two files on the root directory:

  • WORKSPACE.bazel: For defining the workspace environment.
  • BUILD.bazel: For defining builds.

Edit the WORKSPACE.bazel as explained in the following step-by-step instructions:

Start by defining the workspace by giving it a name. Preferably the name of the directory you are currently working at.

    name = "your_workspace_name",
  • Load the http_archive package and define it:

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

    name = "build_bazel_rules_nodejs",
    sha256 = "c29944ba9b0b430aadcaf3bf2570fece6fc5ebfb76df145c6cdad40d65c20811",
    urls = [""],
  • Load the Bazel Node.js rules dependencies and call the function after loading:


  • Load Node.js from node_repositories and call it too:

load("@build_bazel_rules_nodejs//:index.bzl", "node_repositories")

  • Load NPM and define the residing place for package.json and package-lock.json:

load("@build_bazel_rules_nodejs//:index.bzl", "npm_install")

    name = "npm",
    package_json = "//:package.json",
    package_lock_json = "//:package-lock.json",

On the project root directory, create a package.json file. Edit the package.json file as below:

    "dependencies": {
        "express":"4.17.3" // for creating a Node.js web server
    "devDependencies": { // jasmine : Bazel's test runner
        "@bazel/jasmine": "5.3.0", 
  • Install the above dependencies using Bazel by running the following command:
bazel run @nodejs_host//:npm -- install

From the above command, Bazel will create a couple of additional directories for managing the Node.js dependencies: package-lock.json and node_modules.

Implementing and Testing a Simple Calculator Application


Let’s now test the create Bazel environment using a Node.js application. On the project root directory, create a directory and name it apps. Inside the apps directory, create a simple_calculator directory. Inside the simple_calculator, create three files:

  • calculator.js : For defining the logic. Edit calculator.js as follows:
module.exports = class Calculator {
    subtract(x,y){ // returning subtraction of two numbers.
        return x - y;
  • calculator.spec.js : For defining the testing logic. Edit calculator.spec.js as follows:
const Calculator = require('./calculator');
const calculator = new Calculator();

it('10 - 4 = 6 >', () => { 
  // testing the result from the calculator class if it will equal 6
    const expected_value = 6;
  • BUILD.bazel : For defining the Bazel build dependencies and steps. Edit BUILD.bazel as follows:

#loading the node dependencies

    visibility = ["//apps/node_web:__pkg__"] 
    #full visibility of the apps folder

    name="calculator_test", # name
    srcs=["calculator.spec.js"], # spec files
    data = [":node_calculator"]

To test the functionality, run the following command:

bazel test //...

Your response should be similar to:

Bazel with Node.js

Exposing the Calculator Application On a Web Server

Let’s Now load the calculator app to the web while implementing the Bazel builds. Create another directory on the apps folder and name it node_web. In the node_web folder, create two files:

  • index.js : For starting the web server and handling routes. Edit the index.js as follows:
const express = require('express');
const Calculator = require('../node_calculator/calculator');

const app = new express();
const calculator = new Calculator();

app.get('/',(req,res) => {
    res.send(`The result of 10 - 4 = ${calculator.subtract(10,4)}`);

app.listen(8080, () => console.log(`listening on port 8080`));
  • BUILD.bazel : For handling the Bazel build steps. Edit the BUILD.bazel as follows:

load("@build_bazel_rules_nodejs//:index.bzl", "nodejs_binary")

    name = "node_web",
    data = [
    entry_point = ":index.js",

Run the project by executing the following command:

bazel run apps/node_web

You will get such a response on the terminal:

Bazel Builds with Node.js

From above, the server is running on port 8080. Proceed to http://localhost:8080. You will get the following calculator response:

Node.js App


This guide helped us create Node.js with Bazel. We were able to configure Bazel, set up Bazel builds, and, most importantly, run tests using Bazel for the Node.js app. I hope you found this guide helpful.

Bazel isn’t the only solution for the automation of building and testing software. Earthly provides a convenient framework to build images or stand-alone artifacts by leveraging containers for the execution of pipelines.

A Earthfile for building, testing, and containerizing our app could look like this:

FROM node:14

    COPY package.json package-lock.json ./
    RUN npm ci

    FROM +deps
    COPY . .
    RUN npm run build

    FROM +build
    RUN npm test

    FROM +build
    ENTRYPOINT ["npm", "start"]
    SAVE IMAGE --push npm-example:latest

Earthly combines the best ideas from Dockerfiles and Makefiles into one specification, making the containers self-contained, repeatable, portable, and parallel.

Earthly Cloud: Consistent, Fast Builds, Any CI
Consistent, repeatable builds across all environments. Advanced caching for faster builds. Easy integration with any CI. 6,000 build minutes per month included.

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Rose Chege %
Rose Chege
Rose is a lover of technology and an upright individual who is not afraid to get out of her comfort zone and try out new programming paradigms.



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