Published Dec 05, 2019
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const promise = new Promise(function(resolve, reject) {
// ...
})
Promise accepts a function as a constructor argument, which is called the
executor function. This function is called by the internal implementation of
the Promise constructor and it is used to allow the constructing code to
manipulate only a limited part of the internal state of the promise under
construction. In other words, it serves as a mechanism to expose the resolve
and reject functions so that they can be invoked to change the internal state
of the object.
The advantage of this is that only the constructing code has access to resolve
and reject and once the promise object is constructed, it can be passed
around safely; no other code will be able to call reject or resolve and
change the internal state of the promise.
Read-only event emitter is a special kind of event emitter which is not possible
to call the emit method (apart from within the function passed to the
constructor)
const EventEmitter = require('events');
module.exports = class Roee extends EventEmitter {
constructor(executor){
super()
const emit = this.emit.bind(this);
this.emit = undefined;
executor(emit);
}
}
const Roee = require('./roee')
const ticker = new Roee(emit => {
let tickCount = 0;
setInterval(() => emit('tick', tickCount++), 1000)
})
module.exports = ticker
const ticker = require('./ticker')
ticker.on('tick', tickCount => console.log(tickCount, 'TICK'));
ticker.emit('something', {}); // this will fail