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Different approach to preventing userland from emitting meta events #98

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merged 2 commits into from
Aug 11, 2022
Merged

Different approach to preventing userland from emitting meta events #98

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acdebcd
Different approach to preventing userland from emitting meta events
lukehorvat Jun 5, 2022
0b2f77e
Ensure that `canEmitMetaEvents` always gets reverted to false
lukehorvat Aug 10, 2022
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50 changes: 30 additions & 20 deletions index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -10,19 +10,13 @@ const resolvedPromise = Promise.resolve();
const listenerAdded = Symbol('listenerAdded');
const listenerRemoved = Symbol('listenerRemoved');

// Define a symbol that allows internal code to emit meta events, but prevents userland from doing so.
const metaEventsAllowed = Symbol('metaEventsAllowed');

let canEmitMetaEvents = false;
let isGlobalDebugEnabled = false;

function assertEventName(eventName, allowMetaEvents) {
function assertEventName(eventName) {
if (typeof eventName !== 'string' && typeof eventName !== 'symbol' && typeof eventName !== 'number') {
throw new TypeError('`eventName` must be a string, symbol, or number');
}

if (isMetaEvent(eventName) && allowMetaEvents !== metaEventsAllowed) {
throw new TypeError('`eventName` cannot be meta event `listenerAdded` or `listenerRemoved`');
}
}

function assertListener(listener) {
Expand Down Expand Up @@ -157,6 +151,14 @@ function defaultMethodNamesOrAssert(methodNames) {

const isMetaEvent = eventName => eventName === listenerAdded || eventName === listenerRemoved;

function emitMetaEvent(emitter, eventName, eventData) {
if (isMetaEvent(eventName)) {
canEmitMetaEvents = true;
emitter.emit(eventName, eventData);
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canEmitMetaEvents = false;
}
}

class Emittery {
static mixin(emitteryPropertyName, methodNames) {
methodNames = defaultMethodNamesOrAssert(methodNames);
Expand Down Expand Up @@ -253,13 +255,13 @@ class Emittery {

eventNames = Array.isArray(eventNames) ? eventNames : [eventNames];
for (const eventName of eventNames) {
assertEventName(eventName, metaEventsAllowed);
assertEventName(eventName);
getListeners(this, eventName).add(listener);

this.logIfDebugEnabled('subscribe', eventName, undefined);

if (!isMetaEvent(eventName)) {
this.emit(listenerAdded, {eventName, listener}, metaEventsAllowed);
emitMetaEvent(this, listenerAdded, {eventName, listener});
}
}

Expand All @@ -271,13 +273,13 @@ class Emittery {

eventNames = Array.isArray(eventNames) ? eventNames : [eventNames];
for (const eventName of eventNames) {
assertEventName(eventName, metaEventsAllowed);
assertEventName(eventName);
getListeners(this, eventName).delete(listener);

this.logIfDebugEnabled('unsubscribe', eventName, undefined);

if (!isMetaEvent(eventName)) {
this.emit(listenerRemoved, {eventName, listener}, metaEventsAllowed);
emitMetaEvent(this, listenerRemoved, {eventName, listener});
}
}
}
Expand All @@ -294,14 +296,18 @@ class Emittery {
events(eventNames) {
eventNames = Array.isArray(eventNames) ? eventNames : [eventNames];
for (const eventName of eventNames) {
assertEventName(eventName, metaEventsAllowed);
assertEventName(eventName);
}

return iterator(this, eventNames);
}

async emit(eventName, eventData, allowMetaEvents) {
assertEventName(eventName, allowMetaEvents);
async emit(eventName, eventData) {
assertEventName(eventName);

if (isMetaEvent(eventName) && !canEmitMetaEvents) {
throw new TypeError('`eventName` cannot be meta event `listenerAdded` or `listenerRemoved`');
}

this.logIfDebugEnabled('emit', eventName, eventData);

Expand All @@ -327,8 +333,12 @@ class Emittery {
]);
}

async emitSerial(eventName, eventData, allowMetaEvents) {
assertEventName(eventName, allowMetaEvents);
async emitSerial(eventName, eventData) {
assertEventName(eventName);

if (isMetaEvent(eventName) && !canEmitMetaEvents) {
throw new TypeError('`eventName` cannot be meta event `listenerAdded` or `listenerRemoved`');
}

this.logIfDebugEnabled('emitSerial', eventName, eventData);

Expand Down Expand Up @@ -359,7 +369,7 @@ class Emittery {
this.logIfDebugEnabled('subscribeAny', undefined, undefined);

anyMap.get(this).add(listener);
this.emit(listenerAdded, {listener}, metaEventsAllowed);
emitMetaEvent(this, listenerAdded, {listener});
return this.offAny.bind(this, listener);
}

Expand All @@ -372,7 +382,7 @@ class Emittery {

this.logIfDebugEnabled('unsubscribeAny', undefined, undefined);

this.emit(listenerRemoved, {listener}, metaEventsAllowed);
emitMetaEvent(this, listenerRemoved, {listener});
anyMap.get(this).delete(listener);
}

Expand Down Expand Up @@ -422,7 +432,7 @@ class Emittery {
}

if (typeof eventName !== 'undefined') {
assertEventName(eventName, metaEventsAllowed);
assertEventName(eventName);
}

count += anyMap.get(this).size;
Expand Down