High-level languages like Java tend to compile the part first, at run time, and then use JIT to compile the previously compiled middleware output into machine language and run it on the machine. This may affect the performance of the operation.
For example, like angular Web applications, angular bootup up, must be in the browser to perform the compilation process, the formation of ordinary JS code, the browser can understand and execute. And this process, if the page is more complex, it will take a lot of time. At this point the AOT concept can be used.
It is simpler to say that the AOT is built by the build tool at a time by the angular code, or such as Vuejs vue components are compiled into JS code, and bundle up, so that the browser opens the page is already built pure JS code, Can greatly improve the efficiency of program operation.
Https://en.wikipedia.org/wiki/Ahead-of-time_compilation
Https://stackoverflow.com/questions/43307970/vue-2-aot-ahead-of-time-compilation
http://blog.mgechev.com/2016/08/14/ahead-of-time-compilation-angular-offline-precompilation/
Aheadof Time compilation (AOT) vs (JIT) Just in time compilation approach