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lib: refactor events.js #36528

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lib: refactor events.js #36528

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206310d
lib: refactor to use optional chaining in events.js
RaisinTen Dec 15, 2020
3f16e73
lib: refactor to use more primordials in events.js
RaisinTen Dec 15, 2020
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46 changes: 27 additions & 19 deletions lib/events.js
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Expand Up @@ -22,7 +22,12 @@
'use strict';

const {
ArrayPrototypeJoin,
ArrayPrototypePush,
ArrayPrototypeShift,
ArrayPrototypeSlice,
ArrayPrototypeSplice,
ArrayPrototypeUnshift,
Boolean,
Error,
ErrorCaptureStackTrace,
Expand All @@ -39,6 +44,7 @@ const {
ReflectApply,
ReflectOwnKeys,
String,
StringPrototypeSplit,
Symbol,
SymbolFor,
SymbolAsyncIterator
Expand Down Expand Up @@ -200,7 +206,7 @@ EventEmitter.init = function(opts) {
this._maxListeners = this._maxListeners || undefined;


if (opts && opts.captureRejections) {
if (opts?.captureRejections) {
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We'll need to benchmark these changes. The entire events.js file is one of the most performance sensitive in core and changes here can have massive impact throughout. Last I benchmarked, optional chaining still had some performance lag that hadn't been fully optimized out. That's not a block on this on it's own but let's be sure to run benchmarks before this lands.

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I'm also not a fan of the optional chaining operator. I think it hinders readability.

if (typeof opts.captureRejections !== 'boolean') {
throw new ERR_INVALID_ARG_TYPE('options.captureRejections',
'boolean', opts.captureRejections);
Expand Down Expand Up @@ -310,16 +316,18 @@ function enhanceStackTrace(err, own) {
} catch {}
const sep = `\nEmitted 'error' event${ctorInfo} at:\n`;

const errStack = err.stack.split('\n').slice(1);
const ownStack = own.stack.split('\n').slice(1);
const errStack = ArrayPrototypeSlice(StringPrototypeSplit(err.stack, '\n'),
1);
const ownStack = ArrayPrototypeSlice(StringPrototypeSplit(own.stack, '\n'),
1);

const [ len, off ] = identicalSequenceRange(ownStack, errStack);
if (len > 0) {
ownStack.splice(off + 1, len - 2,
' [... lines matching original stack trace ...]');
ArrayPrototypeSplice(ownStack, off + 1, len - 2,
' [... lines matching original stack trace ...]');
}

return err.stack + sep + ownStack.join('\n');
return err.stack + sep + ArrayPrototypeJoin(ownStack, '\n');
}

EventEmitter.prototype.emit = function emit(type, ...args) {
Expand Down Expand Up @@ -437,9 +445,9 @@ function _addListener(target, type, listener, prepend) {
prepend ? [listener, existing] : [existing, listener];
// If we've already got an array, just append.
} else if (prepend) {
existing.unshift(listener);
ArrayPrototypeUnshift(existing, listener);
} else {
existing.push(listener);
ArrayPrototypePush(existing, listener);
}

// Check for listener leak
Expand Down Expand Up @@ -542,7 +550,7 @@ EventEmitter.prototype.removeListener =
return this;

if (position === 0)
list.shift();
ArrayPrototypeShift(list);
else {
if (spliceOne === undefined)
spliceOne = require('internal/util').spliceOne;
Expand Down Expand Up @@ -670,7 +678,7 @@ function arrayClone(arr) {
case 5: return [arr[0], arr[1], arr[2], arr[3], arr[4]];
case 6: return [arr[0], arr[1], arr[2], arr[3], arr[4], arr[5]];
}
return arr.slice();
return ArrayPrototypeSlice(arr);
}

function unwrapListeners(arr) {
Expand Down Expand Up @@ -706,9 +714,9 @@ function getEventListeners(emitterOrTarget, type) {
}

async function once(emitter, name, options = {}) {
const signal = options ? options.signal : undefined;
const signal = options?.signal;
validateAbortSignal(signal, 'options.signal');
if (signal && signal.aborted)
if (signal?.aborted)
throw lazyDOMException('The operation was aborted', 'AbortError');
return new Promise((resolve, reject) => {
const errorListener = (err) => {
Expand Down Expand Up @@ -762,7 +770,7 @@ function eventTargetAgnosticRemoveListener(emitter, name, listener, flags) {

function eventTargetAgnosticAddListener(emitter, name, listener, flags) {
if (typeof emitter.on === 'function') {
if (flags && flags.once) {
if (flags?.once) {
emitter.once(name, listener);
} else {
emitter.on(name, listener);
Expand All @@ -779,7 +787,7 @@ function eventTargetAgnosticAddListener(emitter, name, listener, flags) {
function on(emitter, event, options) {
const { signal } = { ...options };
validateAbortSignal(signal, 'options.signal');
if (signal && signal.aborted) {
if (signal?.aborted) {
throw lazyDOMException('The operation was aborted', 'AbortError');
}

Expand All @@ -791,7 +799,7 @@ function on(emitter, event, options) {
const iterator = ObjectSetPrototypeOf({
next() {
// First, we consume all unread events
const value = unconsumedEvents.shift();
const value = ArrayPrototypeShift(unconsumedEvents);
if (value) {
return PromiseResolve(createIterResult(value, false));
}
Expand All @@ -813,7 +821,7 @@ function on(emitter, event, options) {

// Wait until an event happens
return new Promise(function(resolve, reject) {
unconsumedPromises.push({ resolve, reject });
ArrayPrototypePush(unconsumedPromises, ({ resolve, reject }));
});
},

Expand Down Expand Up @@ -873,18 +881,18 @@ function on(emitter, event, options) {
}

function eventHandler(...args) {
const promise = unconsumedPromises.shift();
const promise = ArrayPrototypeShift(unconsumedPromises);
if (promise) {
promise.resolve(createIterResult(args, false));
} else {
unconsumedEvents.push(args);
ArrayPrototypePush(unconsumedEvents, args);
}
}

function errorHandler(err) {
finished = true;

const toError = unconsumedPromises.shift();
const toError = ArrayPrototypeShift(unconsumedPromises);

if (toError) {
toError.reject(err);
Expand Down