pending


Package defines pending value abstraction in form of three [polymorphic
methods][method], where each one can be extended per type. This abstraction
likely to be used in conjunction with [watchable][watchable].

$3

pending/is module provides method that must return true for all
pending values and return false for all others. Method has default
implementation that returns false. Types that wish to implement this
abstraction should return true while value is considered pending.

``js
var isPending = require("pending/is")

function Pending() {
this._result = this
this._pending = true
this._listeners = []
}
isPending.define(Pending, function(value) {
return value._pending
})

isPending(5) // => false
isPending({}) // => false
isPending(new Pending) // => true
`

$3

pending/await module provides method that can be used to register
listener that must be called once value is no longer pending. Method has
default implementation that calls listener immediately with a value since non
of the built-in types considered to be pending. Custom types wishing to
implement this abstraction should define this method such that all registered
listeners will be invoked with a delivery value once they it transitions to
non-pending state.

`js
var await = require("pending/await")
await(3, console.log) // => info: 3
await({}, console.log) // => info: {}

await.define(Pending, function(value, handler) {
if (!isPending(value)) handler(value._result)
else if (!~value._listeners.indexOf(handler)) value._listeners.push(handler)
})
`

$3

pending/deliver module provides method that can is supposed
to doliver pending values and transition them form pending to non-pending
state, such transition supposed to happen only once. Method does not comes
with default implementation as non of the built-ins are considered pending,
there for attempt to call it on values that don't implement it will throw.
Custom types wishing to implement pending abstraction may choose to implement
it, although it's optional since some pending values may be observable but not
deliverable.


`js
var deliver = require("pending/deliver")
deliver.define(Pending, function(value, result) {
// Ignore delivery for no longer pending values, or
// if value delivery is already in progress.
if (isPending(value) && value._result === value) {
// Empty listeres array to allow registration of new listeners
// in side effect to dispatch, in order to guarantee FIFO order.
var count = 0
var index = 0
var listeners
value._result = result
while (index <= count) {
if (index === count) {
listeners = value._listeners.splice(0)
count = listeners.length
index = 0
if (count === index) {
value._pending = false
index = index + 1
}
} else {
listenersindex
index = index + 1
}
}
}
})
``

Install

npm install pending

[watchable]:https://github.com/Gozala/watchable