whenthen

Holds function executions back until a certain requirement is met

whenthen

A "whenthen" holds function executions back until it has been resolved by a (asynchronous) "worker" function and optionally passes arguments to all the held-back functions. Once the "whenthen" has been resolved all functions will be executed immediately, even those added after it's been resolved.

It is particularly useful when functions have to wait until something happened, or wait for data to become available.

npm install whenthen

Returns a new object that can be used to hold back functions until the worker has resolved. If provided, the worker will be executed the first time a function is added using .do().

The worker will receive a function resolve as its only argument that can be used to resolve the "whenthen". All arguments passed to resolve will be passed on to every task function.

Adds a task function to the "whenthen". The function will be held back until the "whenthen" has been resolved.

Resolves the "whenthen". All arguments passed passed to .resolve will be passed on to every task function.

This can be used as an alternavie to passing a worker function to whenthen().

Run the functions doStuff and doMoreStuff only after fakeAsyncLogin is done:

var whenthen = require('whenthen');
 
var whenLoggedIn = whenthen(function (resolve) {
  setTimeout(function fakeAsyncLogin () {
    console.log('Logged in')
    resolve();
  }, 1000);
});
 
whenLoggedIn.do(function doStuff () {
  console.log('Doing stuff after logged in');
});
 
whenLoggedIn.do(function doMoreStuff () {
  console.log('Doing more stuff after logged in');
});

Run doStuffWithData and doMoreStuffWithData after fakeFetchSomeData has some data:

var whenthen = require('whenthen');
 
var whenDataReady = whenthen(function (resolve) {
  setTimeout(function fakeFetchSomeData () {
    console.log('Fetched some data');
    resolve(null, { x: 100, y: 200});
  }, 2000);
});
 
whenDataReady.do(function doStuffWithData (errdata) {
  if (err) { return console.log('O-oh', err); }
 
  console.log('X is', data.x);
});
 
whenDataReady.do(function doMoreStuffWithData (errdata) {
  if (err) { return console.log('O-oh', err); }
 
  console.log('Y is', data.y);
});

Alternatively resolve then whenthen from outside using .resolve():

var whenKittensBorn = whenthen();
 
whenKittensBorn.do(function announceKittens (date) {
    console.log('Kittens born', date);
});
 
console.log('Waiting for kittens birth');
setTimeout(function awaitKittens () {
    whenKittensBorn.resolve(Date.now());
}, 3000);

Copyright (c) 2012 Max Kueng

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