`import defer` implementation tracker

[robpalme]

This issue is to link to various tooling and runtime implementations.

Tools

• Acorn: acorn-import-phases plugin
• Babel 7.23 via @babel/plugin-proposal-import-defer
  • Implement import defer parsing support babel/babel#15845
  • Implement import defer proposal transform support babel/babel#15878
  • Transform only works for CommonJS output
• Biome 2.1.3
  • 📎 Add support for the defer attribute in import statements biomejs/biome#4215
  • feat(parser): support import defer biomejs/biome#6949
• esbuild 0.25.7
  • Feature Request: import defer evanw/esbuild#4238
  • evanw/esbuild@fc3da57
  • Syntax only, no transform
• Oxc 0.71.0
  • Missing phase: "defer" in ESTree AST oxc-project/oxc#10978
  • feat(ast/estree): add phase field to ImportDeclaration in ESTree AST oxc-project/oxc#11157
• Prettier 3.1.0
  • Update @babel/parser to v7.23.0 prettier/prettier#15471
  • Support deferred import evaluation and source phase import syntax prettier/prettier#15487
• Rolldown TBD
  • [Feature Request]: import defer rolldown/rolldown#4857
• Rollup TBD
  • Import defer support rollup/rollup#5932
• Rspack v1.6.0-beta.1
  • [Feature]: Support for Deferring Module Evaluation (import defer) web-infra-dev/rspack#10608
  • feat: support defer import web-infra-dev/rspack#11871
  • Experimental via experiments.deferImport: true
  • Dynamic import.defer form not implemented
• SWC 1.12.14
  • Support for parsing source phase dynamic imports swc-project/swc#10843
  • feat(es/ast): Support import phase swc-project/swc#8279
  • feat(es/parser): Enable support for dynamic import with defer phase swc-project/swc#10845
• TypeScript 5.9 Beta
  • import defer Stage 3 proposal support microsoft/TypeScript#59391
  • Add support for import defer proposal microsoft/TypeScript#60757
  • Syntax only, no transform
• webpack 5.100 [experiment] implement tc39 Defer Module Evaluation webpack/webpack#16567
  • Experimental via experiments.deferImport: true
  • Dynamic import.defer form not implemented

JS Engines

• JSC
  • [JSC] Add parsing for deferred import proposal WebKit/WebKit#36664
  • [JSC] Add core semantics of import defer WebKit/WebKit#40453
• SpiderMonkey tracker: https://bugzilla.mozilla.org/show_bug.cgi?id=1898544
  • https://bugzilla.mozilla.org/show_bug.cgi?id=1952263
• V8 tracker: https://issues.chromium.org/issues/398218423
  • Merged: https://chromium-review.googlesource.com/c/v8/node-ci/+/7053403
  • Merged: https://chromium-review.googlesource.com/c/v8/v8/+/7247865
  • https://chromium-review.googlesource.com/c/v8/v8/+/7488270

[ardaorkin]

So, can we start to use import defer on production codebase now?

[acutmore]

Hi @ardaorkin, you can use the feature in build tooling that has implemented it. Such as WebPack. But the feature is not yet available natively in browsers.

[ardaorkin]

Thank you for the information @acutmore ! Is there a place where I can track this feature's browser compatibility? Would it be enough if I just check caniuse.com ?

[acutmore]

Subscribing to this issue and periodically checking canIUse or Baseline would be my recommendation.