| 30 Nov 2020 |
 webstrand (Gitter) | *builtin type-safe way | 19:48:30 |
 Jason Kratzer (Gitter) | doesn't that seem crazy that 'in' can't be used to narrow this type? | 19:50:08 |
| Jason Kratzer (Gitter) | and you mean like this?if ('value' in x[key]) {
console.log((x[key] as { value: string}).value)
}
| 19:50:16 |
| Jason Kratzer (Gitter) | (edited) ... {
console.log((x[key] as { value: string}).value)
}
``` => ... {
console.log((x[key] as { value: string}).value)
}
``` | 19:50:22 |
| webstrand (Gitter) | yeah. I understand there are some technical difficulties that make this kind of narrowing difficult, or at least difficult to do with reasonable performance | 19:50:58 |
| webstrand (Gitter) | alternatively console.log((x[key] as typeof x['foo']).value) | 19:51:51 |
|  Instant Kafka (Gitter) joined the room. | 20:16:26 |
| Instant Kafka (Gitter) | Hi. Has anybody ever tried creating a mixin to add an overload to an existing interface? | 20:16:27 |
| webstrand (Gitter) | Yeah, I've done that | 20:16:47 |
| Instant Kafka (Gitter) | I'm trying to add an overload to EventTarget.AddEventListener that takes an event class instead of a string. | 20:17:03 |
| webstrand (Gitter) | Oh, that kind of mixin.
You can use declaration merging to add onto existing interfaces | 20:17:53 |
| Instant Kafka (Gitter) | Maybe I'm overthinking it, but I'd like to avoid the magic strings in Add/RemoveEventListener methods. | 20:18:11 |
| webstrand (Gitter) | Is EvenTarget the DOM one or from Node.js? I can never remember | 20:18:46 |
| Instant Kafka (Gitter) | DOM | 20:18:50 |
| Instant Kafka (Gitter) | I want to apply the mixin to multiple classes and have the mixin call the original implementation from each class. | 20:19:53 |
| *  Resynth (Gitter) is skeptical: be careful when extending native interfaces. | 20:20:17 |
| Instant Kafka (Gitter) | Yeah, after struggling with it for an hour or so, I'm skeptical too. | 20:20:37 |
| webstrand (Gitter) | What he's doing should be fine | 20:20:43 |
| webstrand (Gitter) | Do you have any example code I can use as a basis? | 20:20:54 |
| Resynth (Gitter) | BTW magic strings are hella useful for strongly typed event emitters, @InstantKafka_twitter | 20:21:01 |
| Instant Kafka (Gitter) | how so? | 20:21:32 |
| Instant Kafka (Gitter) | '''
addEventListener(type: { name: string }, listener: EventListenerOrEventListenerObject, options?: boolean | AddEventListenerOptions): void {
(this as EventTarget).addEventListener(stringOrClassName(type), listener, options);
}
''' | 20:25:54 |
| Instant Kafka (Gitter) | hrmm... | 20:25:59 |
| Instant Kafka (Gitter) | (edited) hrmm... => ```
addEventListener(type: { name: string }, listener: EventListenerOrEventListenerObject, options?: boolean | AddEventListenerOptions): void {
(this as EventTarget).addEventListener(stringOrClassName(type), listener, options);
}
``` | 20:26:10 |
| Instant Kafka (Gitter) | stringOrClassName() returns the value of the .name property if it exists or the value if it's a string. | 20:27:00 |
| Instant Kafka (Gitter) | And another overload that takes a string or { name: string } for the type. | 20:29:08 |
| webstrand (Gitter) | for instanceclass PotatoGun extends triggerMixin(EventTarget) {
}
function triggerMixin<T extends new (...args: any[]) => EventTarget>(cons: T) {
return class trigger extends cons {
addEventListener(type: "fire", listener: (this: PotatoGun, ev: ["fireEvent"]) => any, options?: boolean | AddEventListenerOptions): void;
addEventListener(type: string, listener: (this: PotatoGun, ...args: any[]) => any, options?: boolean | AddEventListenerOptions): void;
addEventListener(type: string, listener: (this: PotatoGun, ...args: any[]) => any, options?: boolean | AddEventListenerOptions): void {
super.addEventListener(type, listener, options);
}
}
}
declare let instance: PotatoGun;
instance.addEventListener("fire", (ev) => {});
| 20:29:24 |
| webstrand (Gitter) | if you don't add the type: string overload, your class becomes difficult to extend with new events | 20:30:07 |
| webstrand (Gitter) | (for instance, a subclass will have a difficult time adding new events) | 20:30:25 |
| webstrand (Gitter) | All that being said, I've gone down the path of using EventTarget, and I gave up and implemented my own event subsystem. | 20:31:07 |
