Converting an old JS project to TS
It is not as daunting as it seems
Having written my previous post on using TypeScript, I felt it was the opportune time to convert an old project to TS.
I decided on my export Figma SVGs via CLI as my first JS-to-TS conversion. I built this about 2 years ago, and hastily shipped it out back then as:
- I wanted to get it out as soon as possible (build fast amirite)
- I didn't know the benefits of TS yet
- Install required dependencies
- Create a tsconfig.json file
- Rename '.js' to '.ts'
- Update package.json entry point
- Fix errors, typing, and refactor
- Update tests and add jest.config (optional)
Converting an old project from JS to TS is not as daunting as it seems. While obviously, my project is a small one compared to way bigger open source projects, the steps are pretty much similar. A PR of the changes I have done to do this conversion can be seen here.
Install the required dependencies
For my project, these are ts-node, tsc, typescript, and ts-jest.
ts-node is the TS version of node, and allows you to execute TS files via
ts-node <filename>.ts. tsc is the TS compiler (which comes included when you install typescript).
ts-jest is the jest transformer that allows jest to test our project after we have converted it to TS.
Create a tsconfig.json file
tsconfig is a configuration file in the root of the TS project. It is used to tell the TS compiler how you want to compile your project.
Rename '.js' to '.ts'
This is a straightforward step as it renames the file type of every file in the project from
.ts. If you have JSX files, you will need to rename them to
I needed to change the entry point of my project from
Fix errors, typing, and refactor
This was the most time-consuming part of the conversion process. As I was using ES6 in my tsconfig, I can now use modules. This meant doing this
import axios from 'axios' instead using require
const axios = require('axios')
I also needed to start typing the arguments used by my functions.
Aside from that, I took the opportunity to refactor several parts of my project. One such refactor was to consolidate the constants used in the project into a single file.
Update tests and add jest.config
jest.config is also necessary as jest will use a preset to use the TS files. I also updated my tests.
To answer what a friend asked on twitter:
Any challenges u met?— Estee Tey (@estee_tey) September 3, 2022
I do not think there were major ones that blocked me from completing this TS conversion. Rather, it was my inexperience in converting a project to TS that I felt was a barrier. I had read several guides to get a bird's eye view of what I needed to do.
I highly recommend you to start using typescript in your project(s) if you have yet to 😁