perf/no-legacy-javascript

Why

Transpiling classes, async functions and optional chaining for browsers nobody uses makes bundles larger and slower to run, and polyfills for Baseline features are downloaded by every visitor.

Fix

Declare browser targets once (a browserslist query such as baseline widely available, or the bundler's build.target), drop blanket polyfill imports (core-js/stable in the entry), and add a polyfill only for a feature you use that is not in your targets. See fe-tooling for the configuration.

Examples

{ "browserslist": ["baseline widely available"] }

Sources

• Chrome for Developers, Legacy JavaScript insight
• web.dev, Baseline

Read it in the terminal

npx github:dawidolko/frontend-skills explain perf/no-legacy-javascript