The default value conservatively considers all files to have side effects.

This file is considered to have no side effects because the AST was empty after parsing finished.

This file was listed as not having side effects by a "package.json" file in one of our containing directories with a "sideEffects" field.

This file was loaded using a data-oriented loader (e.g.

Same as above but it came from a plugin.

The module will be bundled CommonJS-style like this: // foo.ts let require_foo = __commonJS((exports, module) => { exports.foo = 123; }); // bar.ts let foo = flag ? require_foo() : null; .

The module will be bundled ESM-style like this: // foo.ts var foo, foo_exports = {}; __export(foo_exports, { foo: () => foo }); let init_foo = __esm(() => { foo = 123; }); // bar.ts let foo = flag ? (init_foo(), __toCommonJS(foo_exports)) : null; .

This contains linker-specific metadata corresponding to a "file" struct from the initial scan phase of the bundler.