Writing fastlane scripts in Javascript

3 Posts back to back!? Yes, lot's of content out there right now.


import { Fastlane } from "fastlanejs";
const flane = new Fastlane();

The longer version

I made a recent post about getting an older react native codebase back up on
fairly new hardware and the next step was to add fastlane to make sure getting
builds for debugging would be easier.

Those who don't know, fastlane is a very extensible tool written to automate
most of the work that you'd do for creating builds and at the end of the day
it's just ruby you can extend it with numerous gem's available online.

Why write it in Javascript then?

Well, you see there's a tiny set of issues that need to be addressed to
understand the usage of js here.

  1. You cannot split lanes into different files
  2. All helper functions have to be defined in the same Fastfile

Now, this isn't a problem everyone would face since not everyone has react
native apps that use the variant approach for creating dev and prod builds
separately. I do and so my Fastfile has quite a bit of code.

These are the functions that my Fastfile has, which are then called by a lane

# ios

# android

the structure is actually very simple, deploy_ functions call the
sign+build functions, then call the dev | prod function based on the
params passed.

fastlane ios dev # would create a dev build
fastlane ios prod # would create an appstore build

Now this is necessary since I deal with apps that aren't just going to be
uploaded to testflight with the prod api, we haves staging servers and the QA
needs to test them so dev builds are unstable/untested and can't be on
testflight, someone's bound to create an accidental release out of it

And when I said multi-variant, there's 2 bundle identifiers created by
com.example.app and com.example.app.dev and the above fastlane lane's take
that into consideration when building. basically each function reads the input

So, there's a few more helper functions to find out if the given parameter is
for dev or prod

let's say the app's ios scheme is named productOne ,then the dev scheme is
named productOneDev

Each of those would create a different build, one would trigger a development
certification signing and upload itself to diawi and notify slack with the link
to the installable app.

The other would upload to testflight and notify slack once the app is out of the
processing phase

Similar flow for android and , this means there's helpers that help with finding
out if the given param was for dev or not

def is_ios_dev(scheme)
    if scheme.end_with("Dev")

def is_android_dev(bundle)
    if bundle.end_with(".dev")

Which can be combined into a single function but it's easier to modify this than
having 2 if conditions nested.

Also, yes I know implicit returns are to be avoided in ruby but that's a pretty
simple function!!

Now, all this is easy and ruby is pretty good language to learn and use but
fastlane doesn't really allow importing ruby files so if I need to modularize
any of this, I either write custom actions that import my ruby code which adds a
lot of glue code but is definitely something I'll be doing to stay close to the
source of the tool.


I like the enthusiasm JS community has to move everything into JS.

Ray Deck decided to create a auto generated
fastlane API layer for javascript. The concept is pretty simple but even better

  1. Run a fastfile with all the actions to generate all the possible inputs and
    outputs into a json file
  2. Setup a tool that can talk to the fastlane runner using the socket server
    that fastlane has
  3. Use the json from the 1st tool to create a typescript api of the same
  4. Wrap this all up in a library and done!

Obviously took a lot of work to get it all working so KUDOS!

Now, I found this library while trying to see if someone had already done it,
because I had a more verbose approach that I was going to take which was writing
a child_process based wrapper for all the fastlane commands that were
documented which would actually be a lot more work than writing something like
this. I'm not very smart...

Now, how does this solve my problem?

We get to write smaller functions that are just that, functions and importable.
Each function is just like an API call to socket server that'll pass in the
parameters as a serialized payload and get the result back and it's all promises
so you can add in more async code.

Let's get to how to use the library.


  1. You still need fastlane so go through their
    docs to set it up
  2. Creating Appfile and Matchfile will reduce the amount of code you write
    in lanes so do keep them intact or write them up first.
npm i fastlanejs
# or
yarn add fastlanejs

Basic Usage

import { Fastlane } from "fastlanejs";

const fastlane = new Fastlane();
(async () => {
  await fastlane.getVersion();
  await fastlane.close();

Real life usage

The API is fully typed so your IDE will help you out a lot with what's valid and
what's not.

Here's what the dev version build I mentioned about above would look like

#!/usr/bin/env node

import { Fastlane } from "fastlanejs";
import process from "node:process";
import dotenv from "dotenv";
import { upload } from "diawi-nodejs-uploader";


// dynamic variables to control behaviour over the file
const isDev = true;
const flane = new Fastlane();
const buildtype = "development";
const scheme = "productDev";
const workspace = "ios/product.xcworkspace";
const project = "ios/product.xcodeproj";
const certType = "development";

await run();

async function run() {
  await flane.updateCodeSigningSettings({
    useAutomaticSigning: false,
    path: project,

  await setup();
  await sign();
  await build();
  const lcRes = await flane.laneContext();
  const lc = JSON.parse(lcRes);

  const uploadResponse = await uploadToDiawi(lc.IPA_OUTPUT_PATH);

  if (!uploadResponse.link) {

  await notifySlack(uploadResponse.link);
  await flane.close();

async function setup() {
  await flane.createKeychain({
    name: process.env.KEYCHAIN_NAME,
    password: process.env.MATCH_PASSWORD,
    unlock: true,

  await flane.match({
    gitUrl: process.env.MATCH_CERTIFICATES_URL,
    teamId: process.env.APPLE_TEAM_ID,
    keychainName: process.env.KEYCHAIN_NAME,
    keychainPassword: process.env.MATCH_PASSWORD,
    readonly: flane.isCi,
    forceForNewDevices: true,
    type: certType,

async function notifySlack(link) {
  const gitBranch = await flane.gitBranch();
  await flane.slack({
    message: "Automation Engine: iOS \n" + link,
    success: true,
    payload: { Git: gitBranch },
    useWebhookConfiguredUsernameAndIcon: true,
    slackUrl: process.env.SLACK_HOOK,

async function uploadToDiawi(filePath) {
  console.log("Uploading to diawi, please wait...");
  const result = await upload({
    file: filePath,
    token: process.env.DIAWI_TOKEN,
    wall_of_apps: "false",

  return result;

async function sign() {
  await flane.registerDevices({
    devicesFile: "./fastlane/devices.txt",
    teamId: process.env.APPLE_TEAM_ID,
  await flane.match({
    gitUrl: process.env.MATCH_CERTIFICATES_URL,
    teamId: process.env.APPLE_TEAM_ID,
    keychainName: process.env.KEYCHAIN_NAME,
    keychainPassword: process.env.MATCH_PASSWORD,
    readonly: flane.isCi,
    forceForNewDevices: true,
    type: certType,

async function build() {
  await flane.incrementBuildNumber({
    buildNumber: process.env.BUILD_NUMBER,
    xcodeproj: project,

  await flane.gym({
    configuration: "Debug",
    workspace: workspace,
    scheme: scheme,
    clean: true,
    outputName: scheme,
    silent: true,
    destination: "generic/platform=iOS",
    outputDirectory: "builds",
    exportMethod: buildtype,

The above handles the following

  1. Creating keychains
  2. Signing the app
  3. Building the app
  4. Uploading it to a distribution system
  5. Notifying slack

and if you closely observe it's only the fastlane's own actions that are
available, plugins like the fastlane_diawi has been replaced with a node
package instead

I can add parameters to each of these functions and export them from a
utils.js file and reuse them to write the prod script with the only things
that change to be the parameters on the top since everything else is being read
from environment variables.

How do I find the parameters I can pass ?

As mentioned, this is all just generated code from the original fastlane
documentation, you can use them and just camelCase the params and you are done.

Overall this is a nice thing for quick fixes and scripts that I would wish to
experiment with and while I've mentioned that I'd like to stay close to the
source, I'll probably write custom actions that'll help me with making it easier
to move a fastlane configuration from one project to another without having to
handle the minor details like bundle identifiers and everything which can be
programmatically extracted (which fastlane already does but no clear API for it

Till then, this seems like a viable option, since I've got generative javascript
code everywhere, writing something similar will be a lot easier.

That's all for now, Adios!