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49 lines
1.8 KiB
Markdown
49 lines
1.8 KiB
Markdown
3 months ago
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# promisify-event
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Gives you a Promise for a specified event on an EventEmitter that is only expected to happen once. Also automatically wires up the `error` event.
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Works with anything that implements the Node.js EventEmitter API (which is pretty much everything other than the DOM).
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Note that this is __not__ suitable for events that are expected to be emitted multiple times, because Promises can only represent one-off successes and failures; if you need a series of values over time, you may want to look at [Promistreams](https://promistream.cryto.net/) and particularly [`@promistream/from-event-emitter`](https://www.npmjs.com/package/@promistream/from-event-emitter) instead.
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## Example
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Also included in the package in runnable form, as `example.js`.
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```js
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"use strict";
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const createEventEmitter = require("create-event-emitter");
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const promisifyEvent = require("./");
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// Demonstrated with a dummy event emitter, but it works with any EventEmitter
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let emitter = createEventEmitter();
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(async function () {
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console.log("waiting...");
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await promisifyEvent(emitter, "test");
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console.log("emitted!");
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})();
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console.log("emitting...");
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emitter.emit("test");
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/* Output:
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waiting...
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emitting...
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emitted!
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*/
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```
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## API
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### promisifyEvent(emitter, eventName)
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- __emitter:__ Any `EventEmitter`. This is the emitter that you want to listen for the event on.
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- __eventName:__ The event name to watch for.
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__Returns:__ A Promise that resolves when the event occurs, or rejects (with the error in question) if an `error` event occurs first.
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Note that when the Promise resolves successfully, it resolves with an *array of* arguments passed to the event callback, as event handlers may receive any number of arguments. It's recommended to use array destructuring syntax to unpack it into variables.
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