Provide SourceTextModule sync versions of link and evaluate methods

What is the problem this feature will solve?

Allow to reimplement require(esm) logic with custom require. Current logic in jest covers only require(cjs) and native modules and to support require(esm) there is need of SourceTextModule sync version with sync link and evaluate methods.

jestjs/jest#15275

What is the feature you are proposing to solve the problem?

linkSync and evaluateSync methods for SourceTextModule or another sync way to programmaticaly create and initialize module.

What alternatives have you considered?

Customization hooks but looks like, according to #56241, there is fundamental problem with implementing evaluation hook for esm modules.

The synchronous linking method is implemented in #59000

I am not sure if evalauteSync is entirely necessary - evaluation is already synchronous if the module does not contain a top-level await and the returned promise would be synchronously fulfilled with undefined, as specified in ECMA262 (in this case, the promise is just like a maybe, you can just assume that it's already fulfilled in synchronous code).

I think to be able to implement userland require(esm) on top of vm.SourceTextModule, there must be a way to detect if the module graph is async (like, if it and its dependencies contain TLA or not), so that a userland framework can do:

function requireEsm() {
  const mod = new vm.SourceTextModule(...);
  mod.linkRequests(mod.moduleRequests.map(resolve));
  mod.instantiate();

  // This is missing
  if (mod.isGraphAsync) {
    throw new Error('Module graph is async');
  }
  mod.evaluate();
  if (mod.status === 'errored') {
    throw mod.error;
  }
  return mod.namespace;
}

vm: expose hasTopLevelAwait on SourceTextModule

benchmark: add benchmark for leaf source text modules

vm: make vm.Module.evaluate() conditionally synchronous

benchmark: add benchmark for leaf source text modules

vm: make vm.Module.evaluate() conditionally synchronous

benchmark: add benchmark for leaf source text modules

vm: make vm.Module.evaluate() conditionally synchronous

benchmark: add benchmark for leaf source text modules

vm: make vm.Module.evaluate() conditionally synchronous

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Provide SourceTextModule sync versions of link and evaluate methods #59656

What is the problem this feature will solve?

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Provide SourceTextModule sync versions of link and evaluate methods #59656

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What is the problem this feature will solve?

What is the feature you are proposing to solve the problem?

What alternatives have you considered?

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joyeecheung commented on Aug 28, 2025

legendecas commented on Aug 29, 2025

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