Angular 5默认编译模式是AOT还是JIT？官方与第三方信息存疑

Great question—this confusion is super common because Angular shifted its default compilation behavior over versions, and sometimes docs can lag a bit or third-party sources oversimplify the details. Let me break this down clearly:

Key Version Breakdown #

• Angular 2 through 4.x: Default compilation for both development and production builds is JIT (Just-in-Time). AOT (Ahead-of-Time) was an optional feature you had to explicitly enable using the --aot flag (e.g., ng build --aot or ng serve --aot).
• Angular 5 and later:
  • Production builds (triggered by ng build --prod, which is the default for ng build in newer CLI versions) use AOT by default.
  • Development builds (like ng serve) still default to JIT, since JIT enables faster hot-reloading during development workflows.

Why the Discrepancy? #

• The Angular docs page you referenced might be focusing on development mode defaults (which are still JIT across all supported versions) or hasn't been fully updated to call out the production build change for newer versions.
• Many third-party posts mix up "default for production" with "overall default"—they're referring to the production build default in Angular 5+, not every build type. Some older posts might also misstate Angular 4's defaults (AOT was never default in Angular 4, even for production).

How to Verify for Your Project #

You can confirm which compilation mode is being used by checking the CLI output when you run a build/serve command:

• Look for lines like AOT compilation enabled in the output to confirm AOT is active.
• For Angular 5+, run ng build (production) and you'll see AOT enabled by default; run ng serve and you'll see JIT in use.
• For Angular 4 or earlier, you'll only see AOT if you add the --aot flag explicitly.

内容的提问来源于stack exchange，提问作者BlueCat