Last modified: March 7, 2018
Angular code must be compiled before it can be interpreted and run in the browser. While Angular has traditionally relied on just in time (JIT) compilation to achieve this, tools like the Angular CLI now make it easy to use ahead of time (AOT) compilation. AOT provides some clear advantages over JIT for optimizing your app to run in the browser. In this article, we discuss the difference between JIT and AOT including the benefits of AOT and how AOT works with Angular.
AOT stands for ahead of time compilation. AOT is not specific to Angular and simply refers to the act of compiling a higher-level language into a binary format that can be executed natively. Using AOT, code is compiled before it is run. This takes a significant amount of work off the runtime engine as the interpreter doesn't need to worry about compiling any assets before the content is ultimately rendered.
At the end fo the day, AOT and JIT do the same things. They both compile your Angular code so it can run in a native environment (aka the browser). The key difference is when the compilation happens. With AOT, your code is compiled before hand. With JIT, your code is compiled at runtime in the browser.
There is little doubt that AOT is the preferred method for compiling and deploying Angular apps. While JIT remains the default method for parsing your Angular code, the performance benefits experienced with AOT along with it's integration into the Angular CLI project make it hard not to use AOT moving forward.