REPL: import statement inside the Node.js REPL

[hemanth]

What is the problem this feature will solve?

Allow import statements in REPL

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

Instead of:

> import assert from 'node:assert'
import assert from 'node:assert'
^^^^^^

Uncaught:
SyntaxError: Cannot use import statement inside the Node.js REPL, alternatively use dynamic import

Can we convert them to dynamic import and execute? Just in the REPL.

Like how top level await was supported in Chrome before TLA was an accepted TC39 proposal.

What alternatives have you considered?

At the least we change the message.

from:

Uncaught:
SyntaxError: Cannot use import statement inside the Node.js REPL, alternatively use dynamic import

to:

Uncaught:
SyntaxError: Cannot use import statement inside the Node.js REPL, alternatively use dynamic import

Instead of:
  import assert from 'node: assert'

use:
 const assert = await import('node: assert')

[aduh95]

Static imports are valid syntax only at the top-level body of a module, so that wouldn't be suited for REPL IIUC.

Like how top level await was supported in Chrome before TLA was an accepted TC39 proposal.

It should be noted that Chrome DevTools still don't let you use static imports in its console.

At the least we change the message.

That sounds like a more reasonable proposal, would you like to submit a PR?

[hemanth]

Sure @aduh95 I can do a PR for this.

[hemanth]

@aduh95 Wondering if we should handle all variations of static imports and convert that to dynamic imports or just show a generic example! 🤷

[aduh95]

There are three types on static import, you don’t have to treat them all the same. If you can show the actual replacement for the user, that’s of course more valuable, but if that’s too difficult it’s ok to use a generic example.

[hemanth]

These four types should be good?

Named import: import { export1, export2 } from "module-name";
Default import: import defaultExport from "module-name";
Namespace import: import * as name from "module-name";
Side effect import: import "module-name";

But then, do we have AST capabilities baked in the source to covert this or do we depend on a robust RE?

[aduh95]

We have acorn

[hemanth]

Added a sample to acron explorer.

import * as name from "module-name"; gets interesting.

[hemanth]

@aduh95 It was easier than expected with acron, not clear on how to import the dep acorn and acorn-walk in repl.js though.

const toDynamicImport = (codeLine) => {
  let dynamicImportStatement = ''
  const ast = acorn.parse(codeSnippet, { sourceType: 'module' });

  walk.ancestor(ast, {
    ImportDeclaration(node, ancestors) {
      const importedModules = node.source.value;
      let importedSpecifiers = node.specifiers.map(specifier => specifier.local.name);

      if (importedSpecifiers.length > 1) {
        importedSpecifiers = `{${importedSpecifiers.join(" ")}}`
      }
      dynamicImportStatement = `const ${importedSpecifiers} = await import('${importedModules}')`;
    },
  });
  return dynamicImportStatement;
} 

self.lines.at(-2) at repl.js#694 will give us the static import lines that the user inputted.

[aduh95]

not clear on how to import the dep acorn and acorn-walk in repl.js though.

We already import it:

node/lib/repl.js

Lines 104 to 107 in 05693ac

	const {
	isIdentifierStart,
	isIdentifierChar,
	} = require('internal/deps/acorn/acorn/dist/acorn');

[hemanth]

Ah, no wonder, it didn't show up for me in search :D

[silverwind]

Static imports are valid syntax only at the top-level body of a module, so that wouldn't be suited for REPL IIUC.

Can't the REPL just be started as a module body instead of current CJS body? require etc still works in modules, so I think it'd a strict superset in terms of features to run the REPL as a module.

Being able to use regular import in the REPL would be a huge QOL improvement.

[aduh95]

Modules are strict mode only, I think that'd be a not-so-nice experience for a REPL.

[silverwind]

I guess strictness exceptions could be made for the REPL. It's meant as a user interface. Either run as a "lax" module or transform the import to dynamic under the hood.

[ljharb]

Anything in the REPL that isn't the same in node code is a potential footgun, or could cause confusion. There's already a few of these things like core modules being implicitly available.

[silverwind]

Anything in the REPL that isn't the same in node code is a potential footgun, or could cause confusion. There's already a few of these things like core modules being implicitly available.

Maybe the REPL could have two modes, a strict one without implicit core module globals, no .help etc, and a lax one with all of these and working import statement.

Though I don't see a use case for strict REPL. If I want strict I run a script instead.

[hemanth]

I like @silverwind's idea. I'm happy to change the PR if we have consensus here.

[silverwind]

Default should be non-strict to not break existing use cases. A --strict-repl could then enable the strict mode that disables all the features.

[aduh95]

Though I don't see a use case for strict REPL. If I want strict I run a script instead.

I very much agree with that, introducing a different kind of REPL seems hardly worth it.

[github-actions]

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[github-actions]

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For more information on how the project manages feature requests, please consult the feature request management document.

[liudonghua123]

Support static import will be convenient for testing some copy/paste pieces of code.

Another alternative tool for this scene is ts-node or tsx or esno, which support static import and typescript and some other features.

[silverwind]

Support static import will be convenient for testing some copy/paste pieces of code.

Another alternative tool for this scene is ts-node or tsx or esno, which support static import and typescript and some other features.

bun repl also has this feature. It's really only node's repl that is seemingly stuck in CJS world.

[liudonghua123]

Support static import will be convenient for testing some copy/paste pieces of code.

Another alternative tool for this scene is ts-node or tsx or esno, which support static import and typescript and some other features.

bun repl also has this feature. It's really only node's repl that is seemingly stuck in CJS world.

yeah, I tried the latest canary windows version of bun, bun repl is still not working. I looking forward the official windows release.

[silverwind]

I think this issue may be a duplicate of #33369, even though this one has a clearer description, so maybe close the other.

[hemanth]

Fix for this was implemented and merged at #48129