typescript es-modules performance lazy-loading

TypeScript 5.9 Beta ships import defer syntax

import defer defers module evaluation until first use, enabling lazy loading without transforming code—only works with namespace imports and requires native runtime support or bundler handling.

Summary

Reduces startup overhead by deferring expensive module initialization until actually accessed; simplifies conditional loading patterns without manual wrapper functions.

Why it matters

Reduces startup overhead by deferring expensive module initialization until actually accessed; simplifies conditional loading patterns without manual wrapper functions.

Implementation verdict

Replaces manual lazy-loading patterns. Requires runtime or bundler supporting deferred evaluation—use only with --module preserve or esnext. Production-ready for modern Node.js; beta status means API surface stable but ecosystem tooling still catching up.

Sources

1.import defer allows you to import a module without immediately executing the module and its dependencies
2.the module is only evaluated on the first use
3.import defer is not transformed or downleveled at all by TypeScript
4.import defer will only work under the --module modes preserve and esnext

Dev Signal

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