Why is tree shaking not removing unused code when using ES6 modules in my JavaScript project?

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Why is tree shaking not removing unused code when using ES6 modules in my JavaScript project?

Asked on Jan 07, 2026

Answer

Tree shaking is a technique used to eliminate dead code in JavaScript projects, especially when using ES6 modules. If it's not working, there could be several reasons. Here's a basic example and some considerations to ensure tree shaking functions correctly.

<!-- BEGIN COPY / PASTE -->
        // utils.js
        export function usedFunction() {
            console.log("This function is used.");
        }

        export function unusedFunction() {
            console.log("This function is not used.");
        }

        // main.js
        import { usedFunction } from './utils.js';

        usedFunction();
        <!-- END COPY / PASTE -->

Additional Comment:

Ensure your build tool (like Webpack, Rollup, or Parcel) is properly configured to support tree shaking.
Use ES6 "import" and "export" syntax, as tree shaking relies on static analysis of these statements.
Check that your build is in "production" mode, as tree shaking is often disabled in "development" mode.
Verify that your modules don't have side effects, as this can prevent tree shaking from removing unused code.

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Why is tree shaking not removing unused code when using ES6 modules in my JavaScript project?

Asked on Jan 07, 2026

Answer

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