Why do we ever need to set "--aot false" in angular prod build?

Question

I know that "ahead of time compilation" provides compilation at the build time. There are also bunch of other advantages of --aot such as

• the application is pre-compiled so there is no such a wait template

• binding errors will be known at build time etc..

However, there is also an option to set --aot to false (for the prod build as well). Why do we ever need to set --aot to false? In other word, what kind of advantage does --jit provides? I just want to understand if there is any disadvantage of using --aot over --jit because otherwise, it sounds like I should always use --aot even in dev build. And if there is no trade-off by using --aot, then why it is not set as default for the ng build and ng serve ?

Answer 1

As @Ingo Burk mentioned in the comment, I end up with same findings so I wanted to post it as an answer.

• Angular 9 actually using AOT as default now.
• AOT takes longer than JIT (so for quick testing to some little fixes, it might be useful)
• The AOT collector only understands a subset of JavaScript. Define metadata objects with the following limited syntax

Also other interesting thing I found out was,

• The AOT compiler does not support function expressions and arrow functions, also called lambda functions.

However In version 5 and later, the compiler automatically performs this rewriting while emitting the .js file