no-side-effects-in-initialization.md

Pattern: Side effect in module initialization

Issue: -

Description

Side effects during module initialization can prevent effective tree-shaking by bundlers. When modules have side effects, bundlers cannot safely eliminate unused code, resulting in larger bundles. Module initialization should be kept pure to allow optimal code elimination.

Examples

Example of incorrect code:

myGlobal = 17; // Cannot determine side-effects of assignment to global variable
const x = { [globalFunction()]: "myString" }; // Cannot determine side-effects of calling global function

Example of correct code:

const localVar = 17; // Local variable assignment, no global side-effects
export default 42; // Pure export with no side-effects