From React to TypeScript, Simplifying Migration with ts-migrate
Tags: typescript, react, javascript, frontend
Published: 2024-06-29 09:42:30

Migrating a React.js project to TypeScript can significantly enhance your codebase by adding static type checking, improving maintainability, and reducing runtime errors. In this article, I will walk you through the migration process using the `ts-migrate` library, covering both full and partial migration approaches.

> **Note:** This article assumes that your project is managed using Yarn instead of npm. If you're using npm, please adjust the commands accordingly.

## Required Libraries
Before starting the migration, make sure you have the following libraries installed:
- `typescript`
- `ts-migrate`
- `@types/react`

You can install these dependencies using Yarn:
```
yarn add typescript ts-migrate @types/react --dev
```

## Migration Process
The `ts-migrate` library provides two options for migration: full migration and partial migration. Full migration converts the entire codebase to TypeScript at once, while partial migration allows you to convert specific parts of the codebase incrementally.

**1. Full Migration**

- Initialize tsconfig file.
Start by initializing the TypeScript configuration file (tsconfig.json) with the following command:


```
yarn tsc --init
```

- Update tsconfig. Replace the content of tsconfig.json with the values from [tsconfig.base.json](https://github.com/airbnb/ts-migrate/blob/master/tsconfig.base.json).

- Run the Migration Command. Execute the full migration using the following command:

```
yarn ts-migrate-full ./
```

- Check for Errors. Start the local server and check for any broken code:

```
yarn dev
```
If any errors are detected, fix them manually until the code runs well.

**2. Partial Migration**

- Initialize tsconfig. Initialize the TypeScript configuration file in the root folder:

```
yarn tsc --init
```

- Update tsconfig. Replace the content of tsconfig.json with the values from [tsconfig.base.json](https://github.com/airbnb/ts-migrate/blob/master/tsconfig.base.json).

- Initialize tsconfig for the Target Folder. Initialize a tsconfig file in the folder you want to migrate:

```
yarn ts-migrate init:extended <folder>
```

- Update Folder-Specific tsconfig. Update the configuration in the newly created tsconfig file according to your needs.

- Run the Migration Command. Migrate the specific folder:

```
yarn ts-migrate-full <folder>
```

- Check for Errors. Start the local server and check for any broken code:

```
yarn dev
```
If any errors are detected, fix them manually until the code runs well.

## Defining Types & Fixing Other Code Issues
After migration, you might encounter some type of errors. Search your codebase for `// @ts-expect-error` comments and fix the corresponding errors as needed.
Here is a step-by-step approach:

**1. Locate Errors**
Search for occurrences of `// @ts-expect-error` in your codebase.

**2. Fix Errors**
Review the errors and define the appropriate types or make necessary code adjustments to resolve them.

## Pros and Cons of Full and Partial Migration
### Full Migration
**Pros:**
- **Consistency**
Ensures the entire codebase is consistent with TypeScript at once.

- **Immediate Benefits**
You get all the benefits of TypeScript (type checking, better tooling, etc.) across your whole project immediately.

- **Simpler Tooling**
Easier to configure tools and build processes for a single codebase language.

**Cons:**

- **High Initial Effort**
Requires significant upfront work to migrate the entire codebase.

- **Potential for Disruption**
Higher risk of introducing bugs or breaking changes in a large migration.

- **Resource Intensive**
May require more resources (time, developers) to complete the migration quickly.

### Partial Migration
**Pros:**
- **Incremental Approach**
Allows gradual migration, reducing immediate workload.

- **Less Risk**
Lower risk of introducing bugs or breaking changes, as you migrate and test small parts of the codebase.

- **Flexible Scheduling**
Easier to fit into regular development cycles without significant disruption.

**Cons:**
- **Mixed Codebase**
You may have a mixed codebase (JavaScript and TypeScript) for a longer period.

- **Complex Tooling**
Requires careful configuration of tools and build processes to handle both JavaScript and TypeScript.

- **Delayed Benefits**
You won’t fully realize the benefits of TypeScript until the entire codebase is migrated.

## Why Use `ts-migrate` Over Manual Migration?
Using `ts-migrate` for your TypeScript migration offers several advantages over manual migration:

**1. Automation**
`ts-migrate` automates many repetitive tasks involved in migrating code to TypeScript. This reduces the time and effort required compared to manual migration, where each file and type definition would need to be handled individually.

**2. Consistency**
The tool ensures a consistent migration approach across your entire codebase. This reduces the risk of human error and helps maintain a uniform coding style, which is harder to achieve with manual migration.

**3. Efficiency**
`ts-migrate` can handle large codebases efficiently. It processes multiple files concurrently, making the migration faster than manually updating each file one by one.

**4. Error Handling**
The tool automatically inserts `// @ts-expect-error` comments where type errors occur, allowing you to identify and fix these issues at your own pace. This helps in managing and prioritizing the resolution of type errors systematically.

**5. Incremental Migration Support**
`ts-migrate` supports both full and partial migration strategies. This flexibility allows you to choose the approach that best suits your project’s size, complexity, and deadlines, something that is more challenging to manage manually.

## Comparison: Manual Migration vs. ts-migrate

| **Feature** | **Manual Migration** | **ts-migrate** |
|------------|----------|-----------|
|**Automation**        | Low - Manual updates needed for each file      | High - Automates repetitive tasks|
| **Consistency**      | Varies - Dependent on individual efforts | High - Ensures consistent migration approach     |
|**Efficiency**      | Low - Time-consuming for large codebases    | High - Processes multiple files concurrently     |
| **Error Handling**     | Manual - Developers must identify and fix errors  | Automated - Inserts `// @ts-expect-error` for easy identification    |
| **Flexibility**     | Low - Full migration is more manual  | High - Supports both full and partial migration|
| **Risk of Human Error**     | High - Prone to inconsistencies | Low - Reduces human error through automation    |

## Choosing the Right Migration Strategy
Deciding between full and partial migration depends on several factors:

**1. Project Size and Complexity**
For large, complex projects, partial migration might be more manageable, allowing you to gradually convert the codebase without overwhelming the team. For smaller projects, full migration can be quicker and more straightforward.

**2. Team Experience and Resources**
Assess your team’s familiarity with TypeScript and available resources. If your team is experienced with TypeScript and you have the capacity to handle a large migration effort, a full migration might be feasible. If your team is less familiar with TypeScript or resources are limited, a partial migration allows for a more controlled and incremental approach.

**3. Project Deadlines and Workflow**
Consider your project timelines and workflow. If you have tight deadlines, partial migration might be less disruptive, allowing you to continue delivering features while gradually introducing TypeScript. Full migration might be suitable if you have a window of time to focus on the migration effort without impacting other deliverables.

**4. Risk Tolerance**
Evaluate your tolerance for potential disruption. Full migration introduces more immediate changes, which can be risky but also delivers immediate benefits. Partial migration spreads the risk over a longer period, providing opportunities to address issues incrementally.

By considering these factors, you can choose the migration strategy that best suits your project’s needs and your team’s capabilities.

## Additional Resources

1. [ts-migrate Repository](https://github.com/airbnb/ts-migrate)
The official GitHub repository for `ts-migrate`, where you can find more information, documentation, and updates about the library.

2. [TS-Migrate: A Tool for Migrating to TypeScript at Scale](https://medium.com/airbnb-engineering/ts-migrate-a-tool-for-migrating-to-typescript-at-scale-cd)
An article by Sergii Rudenko from The Airbnb Tech Blog provides an in-depth look at the ts-migrate tool and its usage.

3. [TypeScript Documentation](https://www.typescriptlang.org/docs/)
The official TypeScript documentation provides comprehensive guides and references for learning TypeScript and integrating it into your projects.

4. [Airbnb's TypeScript Style Guide](https://github.com/airbnb/javascript/tree/master/typescript)
Airbnb's style guide for TypeScript provides best practices and guidelines for writing consistent and maintainable TypeScript code.