How to Build Node.js Application with Bazel

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.

Prerequisites

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.

workspace(
    name = "your_workspace_name",
)

• Load the http_archive package and define it:

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

http_archive(
    name = "build_bazel_rules_nodejs",
    sha256 = "c29944ba9b0b430aadcaf3bf2570fece6fc5ebfb76df145c6cdad40d65c20811",
    urls = ["https://github.com/bazelbuild/rules_nodejs/releases/download/5.7.0/rules_nodejs-5.7.0.tar.gz"],
)

• Load the Bazel Node.js rules dependencies and call the function after loading:

load("@build_bazel_rules_nodejs//:repositories.bzl",\
 "build_bazel_rules_nodejs_dependencies")

build_bazel_rules_nodejs_dependencies()

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

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

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")

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:

{
    "name":"your_project_name",
    "version":"0.0.1",
    "dependencies": {
        "express":"4.17.3" // for creating a Node.js web server
    },
    "devDependencies": { // jasmine : Bazel's test runner
        "@bazel/jasmine": "5.3.0", 
        "jasmine":"4.0.2",
        "jasmine-core":"4.0.1"
    }
}

• 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;
    expect(calculator.subtract(10,4)).toEqual(expected_value);
})

• BUILD.bazel : For defining the Bazel build dependencies and steps. Edit BUILD.bazel as follows:

load("@npm//@bazel/jasmine:index.bzl","jasmine_node_test") 
#loading the node dependencies

filegroup(
    name="node_calculator",
    srcs=["calculator.js"],
    visibility = ["//apps/node_web:__pkg__"] 
    #full visibility of the apps folder
)

jasmine_node_test(
    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:

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")

nodejs_binary(
    name = "node_web",
    data = [
        "//apps/node_calculator:node_calculator",
        "@npm//express:express"
    ],
    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:

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

Conclusion

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. Happy Go coding!