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name: es-modules description: "Use when reviewing scripts, client components, bundles, or runtime behavior related to Use ES modules (import/export). Inspect both source code and the browser execution path so fixes target the real bottleneck or bug." metadata: category: javascript priority: high difficulty: beginner estimatedTime: "15" source: frontendchecklist.io url: https://frontendchecklist.io/rules/javascript/es-modules

Use ES modules (import/export)

ES modules are statically analyzable — bundlers can determine at build time what code is actually used and eliminate the rest (tree-shaking). CommonJS require() is dynamic and prevents this optimization. ES modules are also the browser-native standard, reducing the need for build-time transformation.

Quick Reference

• Use import/export syntax instead of require()/module.exports
• Named exports improve IDE autocompletion and enable tree-shaking
• Add type="module" to script tags or use a bundler to load ES modules in browsers
• Default exports are fine but named exports scale better in large codebases

Check

Identify any use of require(), module.exports, or exports in this JavaScript file that should be converted to ES module syntax.

Fix

Convert all require() and module.exports statements to ES module import/export syntax.

Explain

Explain the benefits of ES modules over CommonJS, including tree-shaking, static analysis, and browser support.

Code Review

Review scripts, client components, and browser execution paths related to Use ES modules (import/export). Flag exact imports, event handlers, runtime side effects, or blocking operations that violate the rule, and state how the change should be verified in the browser.

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For full implementation details, code examples, and framework-specific guidance, see references/rule.md.

Rule page: https://frontendchecklist.io/rules/javascript/es-modules