# Verifying swc minifier using dbg-swc


Everyone wants a faster build.
But **the build time should never be the highest priority**.
There are many more important things - namely correctness and user experience.
In this article, I'll describe a way to _verify_ if the SWC minifier is better than the `terser` for **your** web application.

The SWC minifier is fast.
Almost everyone reading this article will know.
But there's a vast inherent problem with JavaScript minification tools.
_Changing_ the minifier is _risky_.
_Changing_ here includes updating.
In other words, upgrading the `terser` may **break your app in production**
This was a case for lots of people, including my colleague.
So using the SWC minifier becomes something you want to avoid trying.
And yes, I admit that there are bugs in the SWC minifier that no one knows.

If the SWC minifier makes your bundle larger, it's also a bug because it degrades the user experience.
So it's also covered by the new tool.

## Automatic reducing

But there's a way to check if the swc minifier will break your application without breaking the production.
Also, You don't need to give me access to the source code.
Additionally, you don't need to investigate the bug by yourself.

Today, I'm introducing `dbg-swc`, which can be used to verify SWC minifier for your application in a semi-automated way.

### How it works

It uses [`creduce`](http://embed.cs.utah.edu/creduce/) internally, a fantastic CLI tool to _reduce_ an input file to have a minimal input file with the same property.
It repeatedly _tries_ the same operation after modifying the input slightly.
The same operation here is the verification implemented by `dbg-swc`.
Currently, there are two modes.
Those are `size` and `semantics`.
I'll describe them in the Usage section.

### Installation

You need to install `creduce` to use the reducer.
To install `creduce`, please see [INSTALL.md](https://github.com/csmith-project/creduce/blob/master/INSTALL.md)

For `dbg-swc` itself, you can download a binary for your platform from https://github.com/swc-project/dbg-swc/releases
After downloading one for your platform, rename it to `dbg-swc`, make it executable (`chmod +x dbg-swc`), and store it in your `PATH`.

### Usage

If you want to find an input that the SWC minifier breaks, you can do

- `dbg-swc es minifier reduce --mode semantics path/to/file_or_dir`

_Disclaimer: This is not 100% correct verification._

If you want to verify that the SWC minifier does not emit a larger output than terser, you can run

- `dbg-swc es minifier reduce --mode size path/to/file_or_dir`

## Conclusion

A single investment can make long-term gains.
I'd recommend running it against your application.