Labs ch-9.1
I have implemented the once method of the eventEmitter to call the event just once and then the listener is removed. However the test is not passing, because the event emitter is undefined in the assertion assert.equal(this, ee). Any hints how to solve it ?
Comments
-
Hello davidwz,
I don't think that you should touch the assertion...
Could you post your code please ?
0 -
Perhaps the error is caused by not assigning the return value of
new EventEmitter()
to the constantee
. You have to keepee
reference to the instance of the event emitter until the assertion finishes.0 -
Thats the code:
'use strict'
const assert = require('assert')
const { EventEmitter } = require('events')const ee = new EventEmitter()
ee.once('tick', ()=>console.log('one time called'))
let count = 0setInterval(() => {
ee.emit('tick');
}, 100)
function listener () {
count++
setTimeout(() => {
assert.equal(count, 1)
assert.equal(this, ee)
console.log('passed!')
}, 250)
}listener()
And thats the error message: AssertionError [ERR_ASSERTION]: undefined == EventEmitter
0 -
@davidwz said:
Thats the code:
'use strict'
const assert = require('assert')
const { EventEmitter } = require('events')const ee = new EventEmitter()
ee.once('tick', ()=>console.log('one time called'))
let count = 0setInterval(() => {
ee.emit('tick');}, 100)
function listener () {
count++
setTimeout(() => {
assert.equal(count, 1)
assert.equal(this, ee)
console.log('passed!')
}, 250)
}listener()
And thats the error message: AssertionError [ERR_ASSERTION]: undefined == EventEmitter
listener
should be passed as event handler to event function such asee.once()
oree.on
. Invoking listener function directly as you did in the code -listener()
will causethis
in the listener function being undefined under strict mode.So let's check this assertion:
asser.equal(this, ee)
this
would be undefined andee
would be the Event Emmitter instance you created before.
As a result, as mentioned in the error message: undefined == EventEmitter which is not true.0 -
Here is my code
'use strict' const assert = require('assert') const { EventEmitter } = require('events') const ee = new EventEmitter() ee.once('tick', listener) let count = 0 setInterval(() => { ee.emit('tick') }, 100) function listener() { count++ setTimeout(() => { assert.equal(count, 1) assert.equal(this, ee) console.log('passed!') }, 250) }
0 -
Thanks a lot !
0 -
@krave is correct
0 -
@davidmarkclements my code is the same as krave, and I receive 'passed!' in the console. However, the process continues to run and I am required to ctrl+c to end it, is this normal?
0
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