Tc-passing NPM

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