Incomplete code for registering an extension in tutorial

The blog post contains an incomplete code for registering an extension in the first part of the Roll your own JavaScript runtime series. It is missing the part where the extension builder expects the extension name to be passed in as an argument to builder.

Following the tutorial to the letter results in a compilation error. This is part of the Adding a basic filesystem API section.

async fn run_js(file_path: &str) -> Result<(), AnyError> {
    let main_module = deno_core::resolve_path(file_path)?;
-    let runjs_extension = Extension::builder()
+    let runjs_extension = Extension::builder("runjs")
        .ops(vec![
            op_read_file::decl(),
            op_write_file::decl(),
            op_remove_file::decl(),
        ])
        .build();
    let mut js_runtime = deno_core::JsRuntime::new(deno_core::RuntimeOptions {
        module_loader: Some(Rc::new(deno_core::FsModuleLoader)),
        extensions: vec![runjs_extension],
        ..Default::default()
    });

Found another issue, this time in the example.js for the Implementing fetch section. content results in a reference error since it's missing the variable declaration. It's added later in the TypeScript implementation.

console.log("Hello", "runjs!");
+ let content;
content = await runjs.fetch(
  "https://deno.land/[email protected]/examples/welcome.ts",
);
console.log("Content from fetch", content);

If you are modifying a blog post, you may want to modify #7 as well.