Minification removes class identifiers causing observable runtime change in Class.name

Start with the linked StackBlitz reproduction and inspect dist/main.js to confirm how the named class is transformed and how its name is observed at runtime. Review @rollup/plugin-terser's handling of class names and the documented keep_classnames workaround; done means the production output no longer causes the reported runtime difference, with regression coverage for class and constructor names.

• Rollup Plugin Name: @rollup/plugin-terser
• Rollup Plugin Version: 1.0.0
• Rollup Version: 4.59.0
• Operating System (or Browser): any
• Node Version: 22.19.0
• Link to reproduction: https://stackblitz.com/edit/rollup-repro-dxhgy1x9?file=dist%2Fmain.js

Description

When using @rollup/plugin-terser, named class declarations are transformed into anonymous class expressions during minification. This causes clazz.name and this.constructor.name to return an empty string ("") instead of the original class name. This results in observable runtime differences between development and production builds.

Behavior

Terser removes the class identifier and converts:

class MyClass {}

into:

class {}

This creates an anonymous class expression.

According to the ECMAScript specification:

ClassDeclaration → has a name
Anonymous ClassExpression → name === ""

Therefore:

clazz.name === ""
this.constructor.name === ""

Why This Is Problematic

This is not just cosmetic minification.

Class.name and constructor.name are frequently used for:

• logging
• debugging
• dependency injection
• metadata systems
• serialization
• runtime introspection

This creates:

• different runtime behavior in dev vs prod
• silent semantic changes
• hard-to-debug production issues

Important Note

I understand that Terser does not guarantee preservation of Function.name.
However, this transformation introduces observable semantic differences between builds, not just identifier mangling.

Workaround

Setting:

terser({ keep_classnames: true })

preserves the expected behavior.