example(core): add example for FS module loading (#13064)

core/examples/fs_module_loader.rs

@@ -0,0 +1,36 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+
+use deno_core::anyhow::Error;
+use deno_core::FsModuleLoader;
+use deno_core::JsRuntime;
+use deno_core::RuntimeOptions;
+use std::rc::Rc;
+
+fn main() -> Result<(), Error> {
+  let args: Vec<String> = std::env::args().collect();
+  if args.len() < 2 {
+    println!("Usage: target/examples/debug/fs_module_loader <path_to_module>");
+    std::process::exit(1);
+  }
+  let main_url = args[1].clone();
+  println!("Run {}", main_url);
+
+  let mut js_runtime = JsRuntime::new(RuntimeOptions {
+    module_loader: Some(Rc::new(FsModuleLoader)),
+    ..Default::default()
+  });
+
+  let runtime = tokio::runtime::Builder::new_current_thread()
+    .enable_all()
+    .build()?;
+
+  let main_module = deno_core::resolve_path(&main_url)?;
+
+  let future = async move {
+    let mod_id = js_runtime.load_main_module(&main_module, None).await?;
+    let _ = js_runtime.mod_evaluate(mod_id);
+    js_runtime.run_event_loop(false).await?;
+    Ok(())
+  };
+  runtime.block_on(future)
+}