How can I assign a TypeScript type for event payloads for a class like EventEmitter?
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I have a class that is just like Node's EventEmitter (it could even be the same class).
How do I type it in such a way that I can specify what the callback type is for each different event name?
For example, I'd like for even "foo" to have a payload of type number, and event "bar" to have a payload of type string, as in:
const emitter = /* get emitter from somewhere. And how would the type definition look like? */
emitter.on('foo', payload => {
/* type of payload is number, enforced by TypeScript */
testNumber('foo') // TS error, 'foo' is not a number
testNumber(payload) // it works, payload is a number
})
emitter.on('bar', payload => {
/* type of payload is string, enforced by TypeScript */
testString(5) // TS error, 5 is not a string
testString(payload) // it works, payload is a string
})
function testNumber( value: number ) {}
function testString( value: string ) {}
How would we define the EventEmitter declaration so that it is possible to define events and their types, and to then let users use those events with the correct type checking?
Maybe there's a way to define the type of EventEmitter such that when I create one I pass a type argument that contains all the expected types?
Is there a way to do it dynamically after creation?
typescript eventemitter
asked Nov 29 '18 at 1:20
trusktrtrusktr
17.6k31116168
add a comment |
I have a class that is just like Node's EventEmitter (it could even be the same class).
How do I type it in such a way that I can specify what the callback type is for each different event name?
For example, I'd like for even "foo" to have a payload of type number, and event "bar" to have a payload of type string, as in:
const emitter = /* get emitter from somewhere. And how would the type definition look like? */
emitter.on('foo', payload => {
/* type of payload is number, enforced by TypeScript */
testNumber('foo') // TS error, 'foo' is not a number
testNumber(payload) // it works, payload is a number
})
emitter.on('bar', payload => {
/* type of payload is string, enforced by TypeScript */
testString(5) // TS error, 5 is not a string
testString(payload) // it works, payload is a string
})
function testNumber( value: number ) {}
function testString( value: string ) {}
How would we define the EventEmitter declaration so that it is possible to define events and their types, and to then let users use those events with the correct type checking?
Maybe there's a way to define the type of EventEmitter such that when I create one I pass a type argument that contains all the expected types?
Is there a way to do it dynamically after creation?
typescript eventemitter
asked Nov 29 '18 at 1:20
trusktrtrusktr
17.6k31116168
add a comment |
I have a class that is just like Node's EventEmitter (it could even be the same class).
How do I type it in such a way that I can specify what the callback type is for each different event name?
For example, I'd like for even "foo" to have a payload of type number, and event "bar" to have a payload of type string, as in:
const emitter = /* get emitter from somewhere. And how would the type definition look like? */
emitter.on('foo', payload => {
/* type of payload is number, enforced by TypeScript */
testNumber('foo') // TS error, 'foo' is not a number
testNumber(payload) // it works, payload is a number
})
emitter.on('bar', payload => {
/* type of payload is string, enforced by TypeScript */
testString(5) // TS error, 5 is not a string
testString(payload) // it works, payload is a string
})
function testNumber( value: number ) {}
function testString( value: string ) {}
How would we define the EventEmitter declaration so that it is possible to define events and their types, and to then let users use those events with the correct type checking?
Maybe there's a way to define the type of EventEmitter such that when I create one I pass a type argument that contains all the expected types?
Is there a way to do it dynamically after creation?
typescript eventemitter
asked Nov 29 '18 at 1:20
trusktrtrusktr
17.6k31116168
I have a class that is just like Node's EventEmitter (it could even be the same class).
How do I type it in such a way that I can specify what the callback type is for each different event name?
For example, I'd like for even "foo" to have a payload of type number, and event "bar" to have a payload of type string, as in:
const emitter = /* get emitter from somewhere. And how would the type definition look like? */
emitter.on('foo', payload => {
/* type of payload is number, enforced by TypeScript */
testNumber('foo') // TS error, 'foo' is not a number
testNumber(payload) // it works, payload is a number
})
emitter.on('bar', payload => {
/* type of payload is string, enforced by TypeScript */
testString(5) // TS error, 5 is not a string
testString(payload) // it works, payload is a string
})
function testNumber( value: number ) {}
function testString( value: string ) {}
How would we define the EventEmitter declaration so that it is possible to define events and their types, and to then let users use those events with the correct type checking?
Maybe there's a way to define the type of EventEmitter such that when I create one I pass a type argument that contains all the expected types?
Is there a way to do it dynamically after creation?
typescript eventemitter
typescript eventemitter
asked Nov 29 '18 at 1:20
trusktrtrusktr
17.6k31116168
asked Nov 29 '18 at 1:20
trusktrtrusktr
17.6k31116168
edited Nov 29 '18 at 1:44
trusktr
asked Nov 29 '18 at 1:20
trusktrtrusktr
17.6k31116168
asked Nov 29 '18 at 1:20
trusktrtrusktr
17.6k31116168
asked Nov 29 '18 at 1:20
trusktrtrusktr
17.6k31116168
17.6k31116168
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
I'd start off with something like this:
interface Events {
foo: number;
}
interface EventEmitter<T> {
on<K extends keyof T>(s: K, listener: (v: T[K]) => void);
emit<K extends keyof T>(s: K, request: T[K]): any;
}
declare const emitter: EventEmitter<Events>;
emitter.on('foo', (payload) => {
console.log(payload);
});
emitter.emit('foo', 1);
Here's an example on TS Playground.
edited Nov 29 '18 at 1:49
trusktr
17.6k31116168
answered Nov 29 '18 at 1:24
fuzzfuzz
15.8k17109187
Awesome! The mapped types are hard to grok, but this is helping me get there. Thanks!
– trusktr
Nov 29 '18 at 1:32
@trusktr Glad I could help.
– fuzz
Nov 29 '18 at 1:34
What if the emitter instance is imported from a module, and I'd like to add a new event and payload type to it? Basically I don't have access to a predefined set ofEvents, and can only import theemitterinstance. Is it possible?
– trusktr
Nov 29 '18 at 1:36
What doesK extends keyof Tmean exactly?
– trusktr
Nov 29 '18 at 1:36
1
@trusktr It's probably best to ask a separate question on here.
– fuzz
Nov 29 '18 at 1:49
|
show 2 more comments
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
I'd start off with something like this:
interface Events {
foo: number;
}
interface EventEmitter<T> {
on<K extends keyof T>(s: K, listener: (v: T[K]) => void);
emit<K extends keyof T>(s: K, request: T[K]): any;
}
declare const emitter: EventEmitter<Events>;
emitter.on('foo', (payload) => {
console.log(payload);
});
emitter.emit('foo', 1);
Here's an example on TS Playground.
edited Nov 29 '18 at 1:49
trusktr
17.6k31116168
answered Nov 29 '18 at 1:24
fuzzfuzz
15.8k17109187
Awesome! The mapped types are hard to grok, but this is helping me get there. Thanks!
– trusktr
Nov 29 '18 at 1:32
@trusktr Glad I could help.
– fuzz
Nov 29 '18 at 1:34
What if the emitter instance is imported from a module, and I'd like to add a new event and payload type to it? Basically I don't have access to a predefined set ofEvents, and can only import theemitterinstance. Is it possible?
– trusktr
Nov 29 '18 at 1:36
What doesK extends keyof Tmean exactly?
– trusktr
Nov 29 '18 at 1:36
1
@trusktr It's probably best to ask a separate question on here.
– fuzz
Nov 29 '18 at 1:49
|
show 2 more comments
I'd start off with something like this:
interface Events {
foo: number;
}
interface EventEmitter<T> {
on<K extends keyof T>(s: K, listener: (v: T[K]) => void);
emit<K extends keyof T>(s: K, request: T[K]): any;
}
declare const emitter: EventEmitter<Events>;
emitter.on('foo', (payload) => {
console.log(payload);
});
emitter.emit('foo', 1);
Here's an example on TS Playground.
edited Nov 29 '18 at 1:49
trusktr
17.6k31116168
answered Nov 29 '18 at 1:24
fuzzfuzz
15.8k17109187
Awesome! The mapped types are hard to grok, but this is helping me get there. Thanks!
– trusktr
Nov 29 '18 at 1:32
@trusktr Glad I could help.
– fuzz
Nov 29 '18 at 1:34
What if the emitter instance is imported from a module, and I'd like to add a new event and payload type to it? Basically I don't have access to a predefined set ofEvents, and can only import theemitterinstance. Is it possible?
– trusktr
Nov 29 '18 at 1:36
What doesK extends keyof Tmean exactly?
– trusktr
Nov 29 '18 at 1:36
1
@trusktr It's probably best to ask a separate question on here.
– fuzz
Nov 29 '18 at 1:49
|
show 2 more comments
I'd start off with something like this:
interface Events {
foo: number;
}
interface EventEmitter<T> {
on<K extends keyof T>(s: K, listener: (v: T[K]) => void);
emit<K extends keyof T>(s: K, request: T[K]): any;
}
declare const emitter: EventEmitter<Events>;
emitter.on('foo', (payload) => {
console.log(payload);
});
emitter.emit('foo', 1);
Here's an example on TS Playground.
edited Nov 29 '18 at 1:49
trusktr
17.6k31116168
answered Nov 29 '18 at 1:24
fuzzfuzz
15.8k17109187
I'd start off with something like this:
interface Events {
foo: number;
}
interface EventEmitter<T> {
on<K extends keyof T>(s: K, listener: (v: T[K]) => void);
emit<K extends keyof T>(s: K, request: T[K]): any;
}
declare const emitter: EventEmitter<Events>;
emitter.on('foo', (payload) => {
console.log(payload);
});
emitter.emit('foo', 1);
Here's an example on TS Playground.
edited Nov 29 '18 at 1:49
trusktr
17.6k31116168
answered Nov 29 '18 at 1:24
fuzzfuzz
15.8k17109187
edited Nov 29 '18 at 1:49
trusktr
17.6k31116168
edited Nov 29 '18 at 1:49
trusktr
17.6k31116168
edited Nov 29 '18 at 1:49
trusktr
17.6k31116168
17.6k31116168
answered Nov 29 '18 at 1:24
fuzzfuzz
15.8k17109187
answered Nov 29 '18 at 1:24
fuzzfuzz
15.8k17109187
answered Nov 29 '18 at 1:24
fuzzfuzz
15.8k17109187
15.8k17109187
Awesome! The mapped types are hard to grok, but this is helping me get there. Thanks!
– trusktr
Nov 29 '18 at 1:32
@trusktr Glad I could help.
– fuzz
Nov 29 '18 at 1:34
What if the emitter instance is imported from a module, and I'd like to add a new event and payload type to it? Basically I don't have access to a predefined set ofEvents, and can only import theemitterinstance. Is it possible?
– trusktr
Nov 29 '18 at 1:36
What doesK extends keyof Tmean exactly?
– trusktr
Nov 29 '18 at 1:36
1
@trusktr It's probably best to ask a separate question on here.
– fuzz
Nov 29 '18 at 1:49
|
show 2 more comments
Awesome! The mapped types are hard to grok, but this is helping me get there. Thanks!
– trusktr
Nov 29 '18 at 1:32
@trusktr Glad I could help.
– fuzz
Nov 29 '18 at 1:34
What if the emitter instance is imported from a module, and I'd like to add a new event and payload type to it? Basically I don't have access to a predefined set ofEvents, and can only import theemitterinstance. Is it possible?
– trusktr
Nov 29 '18 at 1:36
What doesK extends keyof Tmean exactly?
– trusktr
Nov 29 '18 at 1:36
1
@trusktr It's probably best to ask a separate question on here.
– fuzz
Nov 29 '18 at 1:49
Awesome! The mapped types are hard to grok, but this is helping me get there. Thanks!
– trusktr
Nov 29 '18 at 1:32
Awesome! The mapped types are hard to grok, but this is helping me get there. Thanks!
– trusktr
Nov 29 '18 at 1:32
@trusktr Glad I could help.
– fuzz
Nov 29 '18 at 1:34
@trusktr Glad I could help.
– fuzz
Nov 29 '18 at 1:34
What if the emitter instance is imported from a module, and I'd like to add a new event and payload type to it? Basically I don't have access to a predefined set of
Events, and can only import the emitter instance. Is it possible?– trusktr
Nov 29 '18 at 1:36
What if the emitter instance is imported from a module, and I'd like to add a new event and payload type to it? Basically I don't have access to a predefined set of
Events, and can only import the emitter instance. Is it possible?– trusktr
Nov 29 '18 at 1:36
What does
K extends keyof T mean exactly?– trusktr
Nov 29 '18 at 1:36
What does
K extends keyof T mean exactly?– trusktr
Nov 29 '18 at 1:36
1
1
@trusktr It's probably best to ask a separate question on here.
– fuzz
Nov 29 '18 at 1:49
@trusktr It's probably best to ask a separate question on here.
– fuzz
Nov 29 '18 at 1:49
|
show 2 more comments
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