continue

Compose chainable async methods.

Install

npm install continue --save

Usage

var Continue = require('continue');
var chain = Continue();
var async = require('async'); // <~~ simply for usage example
 
// Add methods to our chain sequence
chain.add('map', function (items, iterator, next) {
  async.map(items, iterator, next);
});
 
chain.add('sortBy', function (items, iterator, next) {
  async.sortBy(items, iterator, next);
});
 
chain.add('filter', function (items, iterator, next) {
  var self = this;
  var error;
  
  async.filter(items, function (item, callback) {
    iterator(item, function (err, matched) {
      if (err) {
        error = err;
        return;
      }
      
      callback(matched);
    });
  }, function (filteredItems) {
    next(error, filteredItems);
  });
});
 
// Use our chain
var list = [
  {
    name: 'John',
    age: 25
  },
  {
    name: 'Jane',
    age: 20
  }
];
 
chain(list)
  .sortBy(function (item, next) {
    next(null, item.age);
  })
  .map(function (item, next) {
    next(null, item.age);
  })
  .then(function (items) {
    // items now equals: [20, 25]
  }, function () {
    // oops, an error may have occured
  });

chain

The instance value returned from calling Continue() is both a function and an object. The object is the instance and the function returns the chain sequence.

chain() supports the follow as initial values to start the chain:

• Primitive - strings, numbers, etc.
• Array - an array of primitives or objects
• Function - a function that is passed a next callback that must be called with the following: next(err, value). The value passed as the second argument becomes the initial value of the chain.

For example:

Primitive

var Continue = require('continue');
var chain = Continue();
 
var someValue = 'my value';
chain(someValue);

Array

var Continue = require('continue');
var chain = Continue();
 
var someValue = [1,2,3,4,5];
chain(someValue);

Function

var Continue = require('continue');
var chain = Continue();
 
chain(function (next) {
  var someValue = 'my value';
  next(null, someValue);
});

instance methods

These methods are available on the chain variable.

add(methodName, methodTask)

Composes a chainable method on the chain. The method is added for all instances of that particular chain.

methodName

A string that will be used as the method name

methodTask

A callback function that is passed the following parameters

• items - any value that you would like passed to the first method in the chain
• iterator - the method called on the value from the previous method that performs some sort of user defined operation
• next - the callback once all items in the list or collection have been processed.

For Example:

var Continue = require('continue');
var chain = Continue();
 
// Add methods to our chain sequence
chain.add('map', function (items, iterator, next) {
  iterator(items, function (err, processItems) {
    next(err, processItems);
  });
});

chain sequence methods

These methods are available on the value returned from called chain(someValue)

The methods available vary according to which methods have been added to the chain. In the usage example above, we've added map, sortBy, and filter. These methods would be available on the chain as well as:

then(successCallback, errorCallback)

Each chain sequence returns a promise. Refer to the Promises/A+ spec for more details.

successCallback

This is called once all chained methods have processed the initial value, unless an error has occurred.

errorCallback

This is called if an error occurs anywhere when processing the initial value in any of the chainable methods. If an error occurs, all processing stops.

For Example:

var Continue = require('continue');
var chain = Continue();
 
var someValue = 'my value';
chain(someValue)
  .someChainableMethod(function (value, next) {
    next(null, value + 's');
  })
  .then(function (processedValue) {
    // processedValue == my values
  });

drain()

Runs each method in the chain b draining the chain queue on next tick.

TODO

• more detailed documentation
• allow callbacks on each chained method
• allow promises to be passed in as inititial value to chain
• Continue module examples

Run Tests

npm install
npm test