Evaluate Module vs Run Script?

[linrongbin16]

Hi, I'm learning the deno_core and the V8 engine inside. I'm confused about the difference between evaluate module and run script.

For example, in the (very simple) Hello, runjs! sample code in Roll your own JavaScript runtime blog.

Roughly speaking (please correct me if I'm wrong), deno_core is doing following steps:

1. load_main_es_module uses the v8::script_compiler::compile_module to compile the main module, and also created all the module dependencies from it (like a dependency tree). At this time, all the modules that stores on local file system is synchronizely loaded, all the remote modules that need to be downloaded is still in fetching status.
2. mod_evaluate uses the v8::Module::evaluate to evalute the main module.
3. run_event_loop start to running the event loop, so all the remote modules can be downloaded, all the async and Promise can be resolved, until the javascript code in the main module been all executed to done.

But, I'm confused that, there's also an API v8::Script::run. Can I simply create a v8 Script and then run it, instead of load ES module and evaluate it?

What's the difference between these two groups of APIs?

1. The module can only be evaluated once, the script can be run multiple times (I think I read this from somewhere).
2. Also here's a guess: the javascript code in a v8 Script is pure tranditional js, it cannot use require or import keywords to import other modules. Correct?

[marvinhagemeister]

This page has more information about the differences between scripts and modules in JavaScript engines https://v8.dev/features/modules

[bartlomieju]

load_main_es_module uses the v8::script_compiler::compile_module to compile the main module, and also created all the module dependencies from it (like a dependency tree). At this time, all the modules that stores on local file system is synchronizely loaded, all the remote modules that need to be downloaded is still in fetching status.

By the time load_main_es_module all remote modules need to be downloaded and loaded into the V8 as well

run_event_loop start to running the event loop, so all the remote modules can be downloaded, all the async and Promise can be resolved, until the javascript code in the main module been all executed to done.

Remote modules are already downloaded, this function keeps going as long as there are async actions pending (think timers, reads from net socket, etc).

Also here's a guess: the javascript code in a v8 Script is pure tranditional js, it cannot use require or import keywords to import other modules. Correct?

Correct

[linrongbin16]

Really thanks for your knowledge sharing and teaching!