promised-until

Transforms a (promised) value until it satisfies the given predicate. Full support for Promises.

Usage

until(predicate, transform)(value) -> Promise(newValue)

Calling until(predicate, transform) returns a function that takes one parameter. Calling that function with value returns a promise, which resolves if predicate(value) is truthy. While predicate(value) is falsey, the value is transformed with transform(value) until predicate(value) returns a truthy value.

predicate(x) -> true|false or Promise(true|false)

A function that accepts one parameter x and returns a truthy or falsey value, or Promise of such a value.

transform(x) -> y or Promise(y)

A function that accepts one parameter x and transforms it into a new value y, or Promise of such a value.

value

The value, or Promise of a value to be transformed.

Example

Non-promised

const until = require('promised-until')

until(
  (c) => c >= 5,
  (c) => c + 1
)(0)
  .then(result => console.log(result)) // logs '5' to the console

Promised

const until = require('promised-until')

until(
  (c) => Promise.resolve(c >= 5),
  (c) => Promise.resolve(c + 1)
)(Promise.resolve(0))
  .then(result => console.log(result)) // logs '5' to the console

Real-world

until(
  (pageToken) => !pageToken
  (pageToken) => {
    return fetchPage(pageToken)
      .then(page => {
        socket.send(page)
        return page.nextPageToken
      })
)(getFirstPageToken())
    .then(() => console.log('done'))

Supported versions

The module is CI-tested with Node versions 0.10, 4.5 (LTS) and the latest (currently 6.5).

Promise implementation

Uses any-promise which defaults to the native Promise implementation. If you want to use a different Promise library, make sure to register it with any-promise. For example require('any-promise/register/bluebird') for bluebird.

For Node versions <= 0.12 a 3rd-party Promise library is required. More details here.