functional-pipeline/README.md

# functional-pipeline

> Quickly chain method calls, property access and functions in natural left to right expression.

It is like [_.invoke](http://lodash.com/docs#invoke) + [_.pluck](http://lodash.com/docs#pluck) +
[_.compose](http://lodash.com/docs#compose) all rolled into single function.


[![NPM][functional-pipeline-icon] ][functional-pipeline-url]

[![Build status][functional-pipeline-ci-image] ][functional-pipeline-ci-url]
[![Coverage Status][functional-pipeline-coverage-image]][functional-pipeline-coverage-url]
[![dependencies][functional-pipeline-dependencies-image] ][functional-pipeline-dependencies-url]
[![devdependencies][functional-pipeline-devdependencies-image] ][functional-pipeline-devdependencies-url]

Install and use under Node:

```
npm install functional-pipeline --save
var fp = require('functional-pipeline');
// or
global.fpDebug = true;
var fp = require('functional-pipeline');
// loads debug version of functional pipeline with
// stricter argument checking and better error reporting
```

Install and use in browser using bower:

```
bower install functional-pipeline
<script src="bower_components/functional-pipeline/dist/fp.js"></script>
// or
<script src="bower_components/functional-pipeline/dist/fp-debug.js"></script>
// attaches as window.fp object
```

## Example

Assuming this common code:

```js
function triple(x) { return 3 * x; }
function add2(x) { return x + 2; }
var data = {
  age: 10,
  getAge: function () { return this.age; }
};
```

You can express in single line

```js
var pipeline = fp('getAge', triple, add2);
```

what usually takes several compositions that are read from inside out

```js
function pipeline(obj) {
  return add2(triple(obj.getAge()));
}
```

You can even use nested paths using '.' separator

```js
var obj = {
  a: {
    b: {
      c: ['foo', 'bar', 'baz']
    }
  }
};
fp('a.b.c.1')(obj); // 'bar'
```

During runtime, detailed meta information is available in the `fp.version` object.

## Why?

Clear code is good code. Functional pipeline makes reading code slightly easier:

* Reading chained pipeline left to right is natural.
* Having no branches (they should be encapsulated inside functions) lowers complexity
* Composing multiple small functions makes code easier to test

I especially recommend using functional pipelines for callbacks,
replacing code with prebuilt and testable pipelines.

Example: lets sort objects in the collection by date nested 2 levels deep. This is
typical of the code arriving from the back end for example. Below
each operation I am showing its order in the callback function. The actual
argument name *item* does not matter.

```js
items = _.sortBy(items, function(item) {
  return new Date(item.latest_event.datetime);
  ------ --------      ------------ --------
     4      3                1         2
});
```

1. Grab `latest_event` property
2. Grab `datetime` property
3. Create `new Date` object from result of the previous step
4. Return the created date.

Reading the steps left to right starting in the middle, then switching
to reading them right to left going back at the start of the line is unnatural to me.
Here is the same sequence using *functional-pipeline*. The return operation is implicit.

```js
function newDate(a) { return new Date(a); }
items = _.sortBy(items, fp('latest_event', 'datetime', newDate));
                           --------------  ----------  -------
                                  1             2         3
```

We had to create a utility function *newDate* to get around JavaScript's `new` keyword.
You could use my [d3-helpers](https://github.com/bahmutov/d3-helpers) library that
provides both functional pipeline and a few small utility functions like `newDate`.

## Debug mode

Creating chains of calls dynamically using strings instead of
actual functions makes debugging harder. Functional pipeline has second implementation
with debugging turned on. This adds stringent checks before calling a method, or
executing a function or returning a non-existent property. For example:

### Checks during pipeline construction

*functional-pipeline debug* script first performs existance check during pipeline
construction, making sure every argument is either a string or a valid function.
If not, a detailed error message is thrown.

```js
global.fpDebug = true;
var fp = require('functional-pipeline');
var f = fp('foo', bar); // bar is non existent function
// throws right away
Error: Invalid arguments to functional pipeline - not a string or function
  0: string foo
  1: undefined argument
```

### Checks during pipeline execution

There are also checks during pipeline execution, throwing detailed error message
if something goes wrong. Both the pipeline setup and the original object is
in the exception's message in addition to the immediate error cause.

```js
var obj = {
  bar: {
    baz: 'baz'
  }
};
var pipeline = fp('bar', 'foo');
pipeline(obj);

Error: Cannot use property foo from object {
  "baz": "baz"
}
pipeline
  0: string bar
  1: string foo
original object
{
  "bar": {
    "baz": "baz"
  }
}
```

## Inspiration

I was inspired by [l33teral](https://github.com/nicholascloud/l33teral) library for
convenient access to properties deep inside object hierarchy. My second inspiration
was [Make tests read like a book](http://uxebu.com/blog/2013/01/08/make-tests-read-like-a-book/) by
Wolfram Kriesing.

Related: [functional-extract](https://github.com/bahmutov/functional-extract)

### Small print

Author: Gleb Bahmutov &copy; 2014

* [@bahmutov](https://twitter.com/bahmutov)
* [glebbahmutov.com](http://glebbahmutov.com)
* [blog](http://glebbahmutov.com/blog/)

License: MIT - do anything with the code, but don't blame me if it does not work.

Spread the word: tweet, star on github, etc.

Support: if you find any problems with this module, email / tweet /
[open issue](https://github.com/bahmutov/functional-pipeline/issues) on Github

## MIT License

Copyright (c) 2014 Gleb Bahmutov

Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation
files (the "Software"), to deal in the Software without
restriction, including without limitation the rights to use,
copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following
conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

[functional-pipeline-icon]: https://nodei.co/npm/functional-pipeline.png?downloads=true
[functional-pipeline-url]: https://npmjs.org/package/functional-pipeline
[functional-pipeline-ci-image]: https://travis-ci.org/bahmutov/functional-pipeline.png?branch=master
[functional-pipeline-ci-url]: https://travis-ci.org/bahmutov/functional-pipeline
[functional-pipeline-coverage-image]: https://coveralls.io/repos/bahmutov/functional-pipeline/badge.png
[functional-pipeline-coverage-url]: https://coveralls.io/r/bahmutov/functional-pipeline
[functional-pipeline-dependencies-image]: https://david-dm.org/bahmutov/functional-pipeline.png
[functional-pipeline-dependencies-url]: https://david-dm.org/bahmutov/functional-pipeline
[functional-pipeline-devdependencies-image]: https://david-dm.org/bahmutov/functional-pipeline/dev-status.png
[functional-pipeline-devdependencies-url]: https://david-dm.org/bahmutov/functional-pipeline#info=devDependencies