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module: do not warn when accessing __esModule of unfinished exports
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Since this property access is performed by generated code, and not
used for accessing the actual exports of a module (and because
transpilers generally define it as the first key of `module.exports`
when it *is* present), it should be okay to allow it.

Refs: #29935
Fixes: #33046

PR-URL: #33048
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Zeyu Yang <himself65@outlook.com>
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addaleax authored and BethGriggs committed Apr 28, 2020
1 parent 4035cbe commit 4abc45a
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Showing 4 changed files with 15 additions and 2 deletions.
7 changes: 5 additions & 2 deletions lib/internal/modules/cjs/loader.js
Original file line number Diff line number Diff line change
Expand Up @@ -824,13 +824,16 @@ function emitCircularRequireWarning(prop) {
// warns when non-existend properties are accessed.
const CircularRequirePrototypeWarningProxy = new Proxy({}, {
get(target, prop) {
if (prop in target) return target[prop];
// Allow __esModule access in any case because it is used in the output
// of transpiled code to determine whether something comes from an
// ES module, and is not used as a regular key of `module.exports`.
if (prop in target || prop === '__esModule') return target[prop];
emitCircularRequireWarning(prop);
return undefined;
},

getOwnPropertyDescriptor(target, prop) {
if (ObjectPrototypeHasOwnProperty(target, prop))
if (ObjectPrototypeHasOwnProperty(target, prop) || prop === '__esModule')
return ObjectGetOwnPropertyDescriptor(target, prop);
emitCircularRequireWarning(prop);
return undefined;
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1 change: 1 addition & 0 deletions test/fixtures/cycles/warning-esm-half-transpiled-a.js
Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
require('./warning-esm-half-transpiled-b.js');
2 changes: 2 additions & 0 deletions test/fixtures/cycles/warning-esm-half-transpiled-b.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
const a = require('./warning-esm-half-transpiled-a.js');
a.__esModule;
7 changes: 7 additions & 0 deletions test/parallel/test-module-circular-dependency-warning.js
Original file line number Diff line number Diff line change
Expand Up @@ -31,3 +31,10 @@ assert.strictEqual(Object.getPrototypeOf(classExport).name, 'Parent');
const esmTranspiledExport =
require(fixtures.path('cycles', 'warning-esm-transpiled-a.js'));
assert.strictEqual(esmTranspiledExport.__esModule, true);

// If module.exports.__esModule is being accessed but is not present, e.g.
// because only the one of the files is a transpiled ES module, no warning
// should be emitted.
const halfTranspiledExport =
require(fixtures.path('cycles', 'warning-esm-half-transpiled-a.js'));
assert.strictEqual(halfTranspiledExport.__esModule, undefined);

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