I was looking into setting up Husky + lint-staged for a new Deno library that I recently open-sourced, when I came across a project called Lefthook. Unlike the duo, this is a single Go binary which can manage git hooks and run commands against staged files. Also unlike the duo, this is agnostic of the project language and doesn’t require having a package.json file. This intrigued me—two birds with one stone and all that.

You can install it in numerous ways—from using curl to fetch it directly to installing with npm. Since I’m using Deno, I did the following:

deno add --dev npm:lefthook

I also had to update my deno.json with the following so that Deno and npm packages play along nicely:

{
    "nodeModulesDir": "auto"
}

I then added the following task in my deno.json to initialize and configure Lefthook:

{
    "tasks": {
        "configure": "lefthook install"
    }
}

After that, I ran deno task configure which initializes Lefthook by adding relevant files into .git/hooks directory. Anyone cloning the project for the first time will have to run deno install followed also by deno task configure.

We could’ve avoided adding configure task by running deno install --allow-scripts to let Lefthook’s postinstall scripts initialize the project. However, using postinstall hooks is discouraged these days due to security concerns and unlike npm, Deno won’t run these scripts by default.

We tell Lefthook what and all to run during hook events by defining them in a lefthook.yaml file. I wanted it to run fmt, lint, check and test commands at pre-commit stage so I configured mine as follows:

pre-commit:
  parallel: true
  commands:
    lint:
      glob: "*.ts"
      run: deno lint {staged_files}
    fmt:
      glob: "*.{ts,md,yaml,json}"
      run: deno fmt --check {staged_files}
    typecheck:
      glob: "*.ts"
      run: deno check {staged_files}
    test:
      glob: "*.ts"
      run: deno test -RW {staged_files}

As I mentioned earlier, Lefthook can replace Husky + lint-staged and it does this via {staged_files} template which is very intuitive in my opinion. I can also filter the files I want to target with the command by configuring the glob property so that deno lint only targets .ts files while fmt can go pretty up the whole project. I also allowed Lefthook to run all these in parallel by setting parallel: true which makes things faster.

Overall, I’m very pleased. The configuration is intuitive and pleasing to maintain. There are plethora of options described in the docs, go take a look if you’re interested. I’m looking forward to using this for more future projects, even the ones not grounded in the JavaScript ecosystem.