systemjs

Enables modern ES module features like top-level await and dynamic imports in browsers as old as IE11, with minimal performance overhead (only ~1.5x slower than native).

Provides built-in support for import maps via script tags, allowing bare specifier mapping to URLs, which simplifies dependency management without build tools.

Optimized for production with benchmarks showing near-native speeds; the s.js loader is only 2.8KB, minimizing bundle bloat.

Hookable architecture allows custom extensions, such as adding AMD support or dynamic import maps through pluggable extras, catering to complex workflows.