Function composition helpers

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Funktional Helper Module
The funktional module provides helper functions for composing functions with different capabilities.


var fn = require("funktional"),
    send = fn.once(console.log.bind(console));

send("foo");    // writes "foo" to console
send("bar");    // does nothing

Helper Functions

bucket(stream.Readable, function) => Promise

Read entire stream and concatenate results. Callback accepts (err, bucket), where bucket is the concatenated result.

ok(function) => function

Wrap function to always insert null as the first argument. Since the first argument is the err for continuation passing style, this has the effect of never generating an error.

once(function) => function

Wrap function to only execute once, always returning the same result.

promise(function) => function

Wrap continuation passing style function to return Promise and accept callback optionally.

pop(array) => function

Generate function which pops a value from an array when called.

push(array) => function

Generate function which pushes a value or values onto an array when called.

razor(function, function) => function

Generate continuation passing style function which passes the results to the first function or the error to the second function.

shift(array) => function

Generate function which shifts values from an array when called.

supervise(childprocess.ChildProcess, function) => Promise

Supervise a child process and collect stdout and stderr data. Callback accepts (err, exit, stdout, stderr), where exit is the exit status, and stdout and stderr are the output streams data.


Generate function which unshifts its arguments onto an array when called.

Appendix: Async Callback Styles

There are three common asynchronous patterns used in node. The funktional module has helpers for wrapping the different styles: continuation passing, promises, or events. These are described here.

Continuation Passing

In the typical node.js continuation passing style, an asynchronous function accepts a callback as its final argument. This callback is called once. The first argument is the error, and subsequent arguments are the results.
// example function in continuation passing style
function continues(a, b, done) { /* ... */ }

// example usage of continuation passing style
continues("apple", 42, function(err, result) {
    if (err) console.error(err);
    else console.log(result);


ECMAScript 6 (Harmony) defines the Promise class, which is an object which wraps an asynchronous operation so that the final error or result can be passed to another function.
// example Promise object
var promise = new Promise( /* ... */ );

// example usage of Promise
promise.then(console.log.bind(console), console.error.bind(console));


Objects with asynchronous methods are often modelled using the EventEmitter class. More than one event may be fired and sometimes no event is fired for a successful operation. Errors are emitted with the "error" event, but results are often just updated on the object. Each EventEmitter is a bit different.
// example EventEmitter
var emitter = new EventEmitter();

// example usage of EventEmitter
emitter.on("result", console.log.bind(console));
emitter.on("error", console.error.bind(console));