p-event 
Promisify an event by waiting for it to be emitted
Useful when you need only one event emission and want to use it with promises or await it in an async function.
Install
$ npm install --save p-event
Usage
const pEvent = require('p-event');
const emitter = require('./some-event-emitter');
pEvent(emitter, 'finish')
// Called when `emitter` emits a `finish` event
.then(result => {
console.log(result);
})
// Called when `emitter` emits an `error` event
.catch(error => {
console.error(error);
});const pEvent = require('p-event');
pEvent(document, 'DOMContentLoaded').then(() => {
console.log('😎');
});API
pEvent(emitter, event, [options])
Returns a Promise that is fulfilled when emitter emits an event matching event, or rejects if emitter emits any of the events defined in the rejectionEvents option.
The returned promise has a .cancel() method, which when called, removes the event listeners and causes the promise to never be settled.
emitter
Type: Object
Event emitter object.
Should have either a .on()/.addListener()/.addEventListener() and .off()/.removeListener()/.removeEventListener() method, like the Node.js EventEmitter and DOM events.
event
Type: string
Name of the event to listen to.
If the same event is defined both here and in rejectionEvents, this one takes priority.
options
Type: Object
rejectionEvents
Type: Array
Default: ['error']
Events that will reject the promise.
Before and after
const fs = require('fs');
function getOpenReadStream(file, callback) {
const stream = fs.createReadStream(file);
stream.on('open', () => {
callback(null, stream);
});
stream.on('error', error => {
callback(error);
});
}
getOpenReadStream('unicorn.txt', (error, stream) => {
if (error) {
console.error(error);
return;
}
console.log('File descriptor:', stream.fd);
stream.pipe(process.stdout);
});const fs = require('fs');
const pEvent = require('p-event');
async function getOpenReadStream(file) {
const stream = fs.createReadStream(file);
await pEvent(stream, 'open');
return stream;
}
getOpenReadStream('unicorn.txt')
.then(stream => {
console.log('File descriptor:', stream.fd);
stream.pipe(process.stdout);
})
.catch(console.error);Related
License
MIT © Sindre Sorhus
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