Caleb CoxC
Deno•15mo ago
Caleb Cox

Iterator is not defined when creating a snapshot with init_ops_and_esm

I've been following the roll your own runtime blog post series to make a simple CLI powered by deno_core. It's worked great, but I'm having trouble on part 3: setting up snapshots. My 
runtime.js
 file is just this:

class StdinIterator extends Iterator {
  next() {
    const line = Deno.core.ops.op_stdin_line();
    if (line === null) {
      return { done: true };
    }
    return { value: line, done: false };
  }
}

globalThis.stdin = new StdinIterator();


In my 
build.rs
, I'm creating the snapshot like this:

create_snapshot(
    CreateSnapshotOptions {
        cargo_manifest_dir: env!("CARGO_MANIFEST_DIR"),
        startup_snapshot: None,
        skip_op_registration: false,
        extensions: vec![kaw::init_ops_and_esm()],
        with_runtime_cb: None,
        extension_transpiler: None,
    },
    None,
)


But I get the error 
Failed to initialize JsRuntime for snapshotting: Uncaught ReferenceError: Iterator is not defined
. Inheriting from 
Iterator
 works fine without using snapshots. Also, I found that switching to 
extensions: vec![kaw::init_ops()]
 in 
build.rs
 when creating the snapshot seems to work fine, but the docs seem to indicate that I should use 
init_ops_and_esm
 when creating the snapshot and 
init_ops
 only when using the snapshot in 
main.rs
.

So my question is is it OK to create the snapshot with 
init_ops
 instead of 
init_ops_and_esm
? If not, is there a way to access 
Iterator
 inside snapshotted code? Thanks in advance for any help! It's been really fun getting Rust and JS working together with deno_core!
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