A command that uses TypeScript to only type check previously passing files

Why?

When integrating TypeScript into a large codebase, using tsc --noEmit type-checks all files and can result in an overwhelming flood of errors. This can make it difficult to spot new errors in files that were previously error-free.

tc-passing records the list of files that pass type check so you can be sure your type safe files remain type safe!

🚀 Install

npm i tc-passing

Note: typescript (or vue-tsc) is assumed to be installed already

Usage

1. Setup (Optional)

You can use tc-passing directly with npx, but for your convenience, it's recommend to add the following commands to your package.json:

{
    "scripts": {
        // ...

        "type-check": "tc-passing",
        "type-check:update": "tc-passing --update"
    },

    "lint-staged": {
        "**/*.{js,ts}": "tc-passing"
    }
}

You can also add it to a commit hook or lint-staged, but note tc-passing does not accept any arguments (e.g. for staged files).

2. Recording passing files

Start by running tc-passing --update to record the list of files that pass type check. This creates a .tc-passing file in your current working directory serving as a baseline for when you type check.

Here's an example of what this file looks like:

# Files passing type check (33.33%) (Generated by tc-passing)
path/to/file-a.ts
path/to/file-b.js

The first line shows a percentage of how much of the codebase is passing.

Make sure to check this file into version control: git add .tc-passing

3. Type check

Simply run tc-passing and it will only type check files in .tc-passing.

Make sure you run tc-passing --update periodically or whenever you fix types in a file.

Type checker

By default, tc-passing will expect you to have typescript installed for tsc. If you have vue-tsc installed, it will use that instead.

FAQ

How does tc-passing compare to tsc-baseline?

Both tools aim to streamline TypeScript integration, but they approach baselining differently:

tsc-baseline

• Focus

  Only show new type errors since last baseline update.

• Baseline file

  JSON file of errors, which can grow large and may lead to merge conflicts in team settings.

• Workflow impact

  Requires frequent updates to maintain an accurate baseline, often necessitating updates with every TypeScript-related commit. Otherwise CI can fail. Running tsc on every commit can slow down development.

tc-passing

• Focus

  Type checking ensures files that were previously passing type checks to remain error-free.

• Baseline file

  List of passing files, which is typically smaller and easier to manage, reducing merge conflicts.

• Workflow impact

  Needs updates less frequently, only necessary when files change from failing to passing, thus streamlining the development process by minimizing the frequency of checks.

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