doc, test: Symbols as event names #4151
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JungMinu
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| const foo = Symbol('foo'); | ||
| let didRun = false; | ||
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| function listener() { |
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You can wrap this in common.mustCall(), then you don't need didRun.
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LGTM with a few comments. |
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Tests aren't happy: @bengl could you please be sure to run |
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| 'use strict'; | |||
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| require('common'); | |||
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I think this needs to be '../common'
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This should be require('../common');
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Fixed the |
| @@ -10,7 +10,8 @@ is opened. All objects which emit events are instances of `events.EventEmitter`. | |||
| You can access this module by doing: `require("events");` | |||
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| Typically, event names are represented by a camel-cased string, however, | |||
| there aren't any strict restrictions on that, as any string will be accepted. | |||
| there aren't any strict restrictions on that, as any string or symbol will be | |||
| accepted. | |||
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Hmm.. is this actually something we want to promote? I know it works but should it. /cc @nodejs/ctc
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It's not documented, but you can emit on objects as well.
const EE = require('events');
const e = new EE();
const b = { foo: 42 };
e.on(b, function() { console.log('hi'); });
e.emit(b);There was a problem hiding this comment.
@trevnorris Sort of. Because b coerces to [object Object], emitting on any object will fire the same event as b.
const EE = require('events');
const e = new EE();
e.on({ foo: 42 }, function() { console.log('hi'); });
e.emit({ bar: 43 }); // hi
e.emit({ baz: 44 }); // hiSymbols don't get coerced for property identifiers though, so they're distinct here I think.
const EE = require('events');
const e = new EE();
const a = Symbol('foo');
e.on(a, function() { console.log('hi'); });
e.emit(Symbol('foo')); // no hiThere was a problem hiding this comment.
hah. nice. never bothered to test that thoroughly.
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Perhaps "any valid property key" is the most correct thing to put here? That encompasses everything that's actually supported and doesn't encourage or discourage the use of Symbols.
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That may be better. I'm wondering too if we shouldn't simply throw if it's anything other than a "valid property key". Passing in an object simply doesn't make sense. Either way tho, this LGTM. Thanks!
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👍 I like the idea of promoting symbol keys because it allows for private events on emitters. |
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@Qard Not really "private". Can still be just as easily accessed via |
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Yeah, private-ish. There's always some escape hatch, isn't there? 😉 |
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Alright I replaced "any string or symbol" with "any valid property key". |
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LGTM |
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@cjihrig .. does this still LGTY? |
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Yes, but I'd still like to see the additional assertion that I originally requested. |
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Yes, thank you! LGTM |
* Document that Symbol can used as event names. * Add test for using Symbol as event names PR-URL: #4151 Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>
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Landed in 7a51878 |
* Document that Symbol can used as event names. * Add test for using Symbol as event names PR-URL: #4151 Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>
* Document that Symbol can used as event names. * Add test for using Symbol as event names PR-URL: #4151 Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>
* Document that Symbol can used as event names. * Add test for using Symbol as event names PR-URL: #4151 Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>
* Document that Symbol can used as event names. * Add test for using Symbol as event names PR-URL: nodejs#4151 Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>
As a result of the new support for Symbols in V8, along with the implementation of EventEmitter in Node, it turns out that Symbols are usable as event names. This adds the possibility of Symbol event names to the docs, and adds an EventEmitter test specific to Symbols so as to ensure that this doesn't break due to any potential future alternative implementations.