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#2413 in Web programming

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42,895 downloads per month
Used in 43 crates (13 directly)

Apache-2.0

3.5MB
93K SLoC

Minifier

EcmaScript minifier for the SWC project. This is basically a port of terser.

Note

Currently name mangler is very simple. To focus on creating a MVP, I (kdy1) will use simple logic for name mangler and implement the content-aware name mangler after publishing first non-beta version.

Debugging tips

If the output contains variables named e, t, n it typically means the original library is published in a minified form and the input contains eval. The current swc name mangler does not do anything if eval is used.

Profiling the minifier

From mac os x, run

./scripts/instrument/all.sh path/to/input/dir

lib.rs:

JavaScript minifier implemented in rust.

Assumptions

Like other minification tools, swc minifier assumes some things about the input code.

  • TDZ violation does not exist.

In other words, TDZ violation will be ignored.

  • Acesssing top-level identifiers do not have side effects.

If you declare a variable on globalThis using a getter with side-effects, swc minifier will break it.

Debugging

In debug build, if you set an environment variable SWC_CHECK to 1, the minifier will check the validity of the syntax using node --check

Cargo features

debug

If you enable this cargo feature and set the environment variable named SWC_RUN to 1, the minifier will validate the code using node before each step.

Dependencies

~9–20MB
~274K SLoC