d7452b7140
Warn when a non-existent property of an unfinished module.exports
object is being accessed, as that very often indicates the presence
of a hard-to-detect and hard-to-debug problem.
This mechanism is only used if `module.exports` is still a
regular object at the point at which the second, circular `require()`
happens.
The downside is that, temporarily, `module.exports` will have a
prototype other than `Object.prototype`, and that there may
be valid uses of accessing non-existent properties of unfinished
`module.exports` objects.
Performance of circular require calls in general is not
noticeably impacted.
confidence improvement accuracy (*) (**) (***)
module/module-loader-circular.js n=10000 3.96 % ±5.12% ±6.82% ±8.89%
Example:
$ cat a.js
'use strict';
const b = require('./b.js');
exports.fn = () => {};
$ cat b.js
'use strict';
const a = require('./a.js');
a.fn();
$ node a.js
(node:1617) Warning: Accessing non-existent property 'fn' of module exports inside circular dependency
/tmp/b.js:4
a.fn();
^
TypeError: a.fn is not a function
at Object.<anonymous> (/tmp/b.js:4:3)
[...]
PR-URL: https://github.com/nodejs/node/pull/29935
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
34 lines
1.3 KiB
JavaScript
34 lines
1.3 KiB
JavaScript
'use strict';
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const common = require('../common');
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const assert = require('assert');
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const fixtures = require('../common/fixtures');
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common.expectWarning({
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Warning: [
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["Accessing non-existent property 'missingPropB' " +
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'of module exports inside circular dependency'],
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["Accessing non-existent property 'Symbol(someSymbol)' " +
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'of module exports inside circular dependency'],
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["Accessing non-existent property 'missingPropModuleExportsB' " +
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'of module exports inside circular dependency']
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]
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});
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const required = require(fixtures.path('cycles', 'warning-a.js'));
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assert.strictEqual(Object.getPrototypeOf(required), Object.prototype);
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const requiredWithModuleExportsOverridden =
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require(fixtures.path('cycles', 'warning-moduleexports-a.js'));
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assert.strictEqual(Object.getPrototypeOf(requiredWithModuleExportsOverridden),
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Object.prototype);
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// If module.exports is not a regular object, no warning should be emitted.
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const classExport =
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require(fixtures.path('cycles', 'warning-moduleexports-class-a.js'));
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assert.strictEqual(Object.getPrototypeOf(classExport).name, 'Parent');
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// If module.exports.__esModule is set, no warning should be emitted.
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const esmTranspiledExport =
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require(fixtures.path('cycles', 'warning-esm-transpiled-a.js'));
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assert.strictEqual(esmTranspiledExport.__esModule, true);
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