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[Backport v14.x] module: add isPreloading indicator #36988

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[Backport v14.x] module: add isPreloading indicator #36988

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c38b2ad
module: add isPreloading indicator
jasnell Nov 25, 2020
4569a65
doc: fix module.isPreloading documentation
aduh95 Jan 15, 2021
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8 changes: 8 additions & 0 deletions doc/api/modules.md
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Original file line number Diff line number Diff line change
Expand Up @@ -889,6 +889,14 @@ added: v0.1.16
The identifier for the module. Typically this is the fully resolved
filename.

### `module.isPreloading`
<!-- YAML
added: REPLACEME
-->

* Type: {boolean} `true` if the module is running during the Node.js preload
phase.

### `module.loaded`
<!-- YAML
added: v0.1.16
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9 changes: 9 additions & 0 deletions lib/internal/modules/cjs/loader.js
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Expand Up @@ -128,6 +128,7 @@ const relativeResolveCache = ObjectCreate(null);

let requireDepth = 0;
let statCache = null;
let isPreloading = false;

function stat(filename) {
filename = path.toNamespacedPath(filename);
Expand Down Expand Up @@ -219,6 +220,10 @@ ObjectDefineProperty(Module, 'wrapper', {
}
});

ObjectDefineProperty(Module.prototype, 'isPreloading', {
get() { return isPreloading; }
});
Comment on lines +223 to +225
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It might be a good idea to also backport NativeModule.prototype.isPreloading:

node/lib/internal/modules/cjs/loader.js

Lines 236 to 238 in e279304

const isPreloadingDesc = { get() { return isPreloading; } };
ObjectDefineProperty(Module.prototype, 'isPreloading', isPreloadingDesc);
ObjectDefineProperty(NativeModule.prototype, 'isPreloading', isPreloadingDesc);


let debug = require('internal/util/debuglog').debuglog('module', (fn) => {
debug = fn;
});
Expand Down Expand Up @@ -1202,6 +1207,8 @@ Module._preloadModules = function(requests) {
if (!ArrayIsArray(requests))
return;

isPreloading = true;

// Preloaded modules have a dummy parent module which is deemed to exist
// in the current working directory. This seeds the search path for
// preloaded modules.
Expand All @@ -1210,11 +1217,13 @@ Module._preloadModules = function(requests) {
parent.paths = Module._nodeModulePaths(process.cwd());
} catch (e) {
if (e.code !== 'ENOENT') {
isPreloading = false;
throw e;
}
}
for (let n = 0; n < requests.length; n++)
parent.require(requests[n]);
isPreloading = false;
};

Module.syncBuiltinESMExports = function syncBuiltinESMExports() {
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2 changes: 2 additions & 0 deletions test/fixtures/ispreloading.js
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@@ -0,0 +1,2 @@
const assert = require('assert');
assert(module.isPreloading);
13 changes: 13 additions & 0 deletions test/parallel/test-preload.js
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Expand Up @@ -27,6 +27,19 @@ const fixtureE = fixtures.path('intrinsic-mutation.js');
const fixtureF = fixtures.path('print-intrinsic-mutation-name.js');
const fixtureG = fixtures.path('worker-from-argv.js');
const fixtureThrows = fixtures.path('throws_error4.js');
const fixtureIsPreloading = fixtures.path('ispreloading.js');

// Assert that module.isPreloading is false here
assert(!module.isPreloading);

// Test that module.isPreloading is set in preloaded module
// Test preloading a single module works
childProcess.exec(
`"${nodeBinary}" ${preloadOption([fixtureIsPreloading])} "${fixtureB}"`,
function(err, stdout, stderr) {
assert.ifError(err);
assert.strictEqual(stdout, 'B\n');
});

// Test preloading a single module works
childProcess.exec(`"${nodeBinary}" ${preloadOption([fixtureA])} "${fixtureB}"`,
Expand Down