function that returns a promise in anticipation of an event
npm install wait-for-event-promiseA simple module that exposes a function used to wait for specific events
from an emitter.
``bash`
npm install wait-for-event-promise
#### waitForEvent(emitter: EventEmitter, eventName: String [, filter: Function, options: Object ])
A minimal example:
`js
const waitForEvent = require('wait-for-event-promise');
const EventEmitter = require('events')
(async function () {
// create event emitter
const emitter = new EventEmitter();
// create a promise for wait for a 'hello' event
const helloPromise = waitForEvent(emitter, 'hello');
// emit a hello event
emitter.emit('hello', {
message: 'world'
});
// promise will resolve with the data that was emit
const event = await helloPromise; // { message: 'world' }
console.log(event.message); // outputs: 'world'
})();
`
A function can be passed into to filter out events that you don't care about.
`js
const emitter = new EventEmitter();
const helloPromise = waitForEvent(emitter, 'hello', (event) => {
return event === 'world';
});
emitter.emit('hello', 'bob');
// we don't care about bob, so helloPromise has not resolved yet
emitter.emit('hello', 'world');
// now helloPromise has resolved
const event = await helloPromise;
console.log(event); // outputs: 'world'
`
Alternatively, a filter can be provided as part of the options object.
`js`
waitForEvent(emitter, 'hello', {
filter: (value) => value === 'world'
});
A timeout can also be used to ensure you don't indefinitely wait on an event.
If the emitter does not emit the proper event before the timeout, the
promise will reject.
`js
const emitter = new EventEmitter();
// wait for 1000 ms before rejecting
const helloPromise = waitForEvent(emitter, 'hello', {
timeout: 1000
});
try {
await helloPromise;
} catch (err) {
// after 1000 ms has passed
console.err(err); // err.message === "Timed out waiting for event"
}
`
A timeout can also be used with a filter function.
`js
waitForEvent(emitter, 'hello', (value) => {
return event === 'hello';
}, { timeout: 1000 });
// alternatively, you can use supply the filter function in the options
waitForEvent(emitter, 'hello', {
timeout: 1000,
filter: (event) => event === 'world'
});
`
A logging function can be passed in to get more information about what
the module is doing.
`js
const helloPromise = waitForEvent(emitter, 'hello', {
logger: console.debug.bind(console),
filter: (event) => event === 'hello'
});
emitter.emit('hi');
emitter.emit('hey');
emitter.emit('yo');
emitter.emit('hello');
`
In your logs, you will see the following output:
`
Waiting for event: hello
Filtering for event: hello
Filtering for event: hello
Filtering for event: hello
Got matching event: hello