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lib, doc: fix AsyncResource.bind not using 'this' from the caller by default #42177

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merged 5 commits into from
Mar 8, 2022
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lib, doc: fix AsyncResource.bind not using 'this' from the caller by default #42177

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f906610
lib: fix AsyncResource.bind not using 'this' from the caller by default
rochdev Mar 1, 2022
280dbb2
doc: update AsyncResource.bind doc to reflect new thisArg behaviour
rochdev Mar 1, 2022
b28e307
lib: refactor AsyncResource.bind to not use globals
rochdev Mar 3, 2022
c172ce2
lib: refactor AsyncResource.bind to reduce number of allocations
rochdev Mar 4, 2022
ab540ff
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aduh95 Mar 7, 2022
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8 changes: 8 additions & 0 deletions doc/api/async_context.md
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Original file line number Diff line number Diff line change
Expand Up @@ -446,6 +446,10 @@ added:
- v14.8.0
- v12.19.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42177
description: Changed the default when `thisArg` is undefined to use `this`
from the caller.
- version: v16.0.0
pr-url: https://github.com/nodejs/node/pull/36782
description: Added optional thisArg.
Expand All @@ -468,6 +472,10 @@ added:
- v14.8.0
- v12.19.0
changes:
- version: REPLACEME
pr-url: https://github.com/nodejs/node/pull/42177
description: Changed the default when `thisArg` is undefined to use `this`
from the caller.
- version: v16.0.0
pr-url: https://github.com/nodejs/node/pull/36782
description: Added optional thisArg.
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23 changes: 14 additions & 9 deletions lib/async_hooks.js
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ const {
ArrayPrototypeIndexOf,
ArrayPrototypePush,
ArrayPrototypeSplice,
ArrayPrototypeUnshift,
FunctionPrototypeBind,
NumberIsSafeInteger,
ObjectDefineProperties,
Expand Down Expand Up @@ -223,15 +224,19 @@ class AsyncResource {
return this[trigger_async_id_symbol];
}

bind(fn, thisArg = this) {
bind(fn, thisArg) {
validateFunction(fn, 'fn');
const ret =
FunctionPrototypeBind(
this.runInAsyncScope,
this,
fn,
thisArg);
ObjectDefineProperties(ret, {
let bound;
if (thisArg === undefined) {
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@aduh95 aduh95 Mar 3, 2022 •
edited
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What if the user would like thisArg to be undefined? I think using arguments.length makes more sense here, I don't see a reason to not let undefined be a valid value for thisArg.
If the doc you say when `thisArg` is not provided, not when `thisArg` is `undefined` .

Suggested change
if (thisArg === undefined) {
if (arguments.length !== 1) {

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This would prevent ever adding any new arguments without a breaking change to allow undefined as I'm doing right now. I think the tradeoff of undefined being a special value makes more sense.

For example:

asyncResource.bind(fn, undefined, 'foo') // potential future API

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@targos targos Mar 4, 2022 •
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We can use if (arguments.length > 1) instead.
Edit: sorry that wouldn't help

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the workaround is to wrap the function to give a special value to this:

ar.bind(function (...args) {
  return fn.call(undefined, ...args);
}, undefined, 'foo');

Which seems ok, and is kind of what has to be done in the cases of default arguments anyway. Default arguments in JS are only on undefined so this seems fine.

const resource = this;
bound = function(...args) {
ArrayPrototypeUnshift(args, fn, this);
return ReflectApply(resource.runInAsyncScope, resource, args);
};
} else {
bound = FunctionPrototypeBind(this.runInAsyncScope, this, fn, thisArg);
}
ObjectDefineProperties(bound, {
'length': {
configurable: true,
enumerable: false,
Expand All @@ -245,7 +250,7 @@ class AsyncResource {
writable: true,
}
});
return ret;
return bound;
}

static bind(fn, type, thisArg) {
Expand Down
7 changes: 6 additions & 1 deletion test/parallel/test-asyncresource-bind.js
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Original file line number Diff line number Diff line change
Expand Up @@ -41,11 +41,16 @@ const fn3 = asyncResource.bind(common.mustCall(function() {
fn3();

const fn4 = asyncResource.bind(common.mustCall(function() {
assert.strictEqual(this, asyncResource);
assert.strictEqual(this, undefined);
}));
fn4();

const fn5 = asyncResource.bind(common.mustCall(function() {
assert.strictEqual(this, false);
}), false);
fn5();

const fn6 = asyncResource.bind(common.mustCall(function() {
assert.strictEqual(this, 'test');
}));
fn6.call('test');