## lodash/fp

The `lodash/fp` module is an instance of `lodash` with its methods wrapped to
produce immutable auto-curried iteratee-first data-last methods.

## Installation

In a browser:
```html
<script src='path/to/lodash.js'></script>
<script src='path/to/lodash.fp.js'></script>
```

In Node.js:
```js
// Load the fp build.
var fp = require('lodash/fp');

// Load a method category.
var object = require('lodash/fp/object');

// Load a single method for smaller builds with browserify/rollup/webpack.
var extend = require('lodash/fp/extend');
```

## Mapping

Immutable auto-curried iteratee-first data-last methods sound great, but what
does that really mean for each method? Below is a breakdown of the mapping used
to convert each method.

#### Capped Iteratee Arguments

Iteratee arguments are capped to avoid gotchas with variadic iteratees.
```js
// The `lodash/map` iteratee recieves three arguments: (value, index|key, collection).
_.map(['6', '8', '10'], parseInt);
// → [6, NaN, 2]

// The `lodash/fp/map` iteratee is capped at one argument: (value).
fp.map(parseInt)(['6', '8', '10']);
// → [6, 8, 10]
```

Methods that cap iteratees to one argument:<br>
<%= toFuncList(_.keys(_.pickBy(mapping.iterateeAry, _.partial(_.eq, _, 1)))) %>

Methods that cap iteratees to two arguments:<br>
<%= toFuncList(_.keys(_.pickBy(mapping.iterateeAry, _.partial(_.eq, _, 2)))) %>

The iteratee of `mapKeys` is invoked with one argument: (key)

#### Fixed Arity

Methods have fixed arities to support auto-currying.
```js
// The `lodash/padStart` method accepts an optional `chars` param.
_.padStart('a', 3, '-')
// → '--a'

// The `lodash/fp/padStart` method does not.
fp.padStart(3)('a');
// → '  a'
fp.padCharsStart('-')(3)('a');
// → '--a'
```

Methods with a fixed arity of one:<br>
<%= toFuncList(mapping.aryMethod[1]) %>

Methods with a fixed arity of two:<br>
<%= toFuncList(mapping.aryMethod[2]) %>

Methods with a fixed arity of three:<br>
<%= toFuncList(mapping.aryMethod[3]) %>

Methods with a fixed arity of four:<br>
<%= toFuncList(mapping.aryMethod[4]) %>

#### Rearranged Arguments

Method arguments are rearranged to make composition easier.
```js
// The `lodash/filter` method accepts (collection, iteratee).
var compact = _.partial(_.filter, _, Boolean);
compact(['a', null, 'c']);
// → ['a', 'c']

// The `lodash/fp/filter` method accepts (iteratee, collection)
var compact = fp.filter(Boolean);
compact(['a', null, 'c']);
// → ['a', 'c']
```

Methods with a fixed arity of two have an argument order of:<br>
<%= toArgOrder(mapping.aryRearg[2]) %>

Methods with a fixed arity of three have an argument order of:<br>
<%= toArgOrder(mapping.aryRearg[3]) %>

Methods with a fixed arity of four have an argument order of:<br>
<%= toArgOrder(mapping.aryRearg[4]) %>

Methods with custom argument orders:<br>
<%= _.map(mapping.methodRearg, function(orders, methodName) {
  return ' * `_.' + methodName + '` has an order of ' + toArgOrder(orders);
}).join('\n') %>

Methods with unchanged argument orders:<br>
<%= toFuncList(_.keys(mapping.skipRearg)) %>

The methods `partial` & `partialRight` accept an array of arguments to partially
apply as their second parameter.

#### New Methods

Not all variadic methods have corresponding new method variants. Feel free to
[request](https://github.com/lodash/lodash/blob/master/.github/CONTRIBUTING.md#feature-requests)
any additions.

Methods created to accommodate Lodash’s variadic methods:<br>
<%= toFuncList(_.keys(mapping.remap)) %>

#### Aliases

There are <%= _.size(mapping.aliasToReal) %> method aliases:<br>
<%= _.map(mapping.aliasToReal, function(realName, alias) {
  return ' * `_.' + alias + '` is an alias of `_.' + realName + '`';
}).join('\n') %>

## Chaining

The `lodash/fp` module **does not** convert chain sequence methods. See
[Izaak Schroeder’s article](https://medium.com/making-internets/why-using-chain-is-a-mistake-9bc1f80d51ba)
for more details.

## Convert

Although `lodash/fp` & its method modules come pre-converted, there are times
when you may want to customize the conversion. That’s when the `convert` method
comes in handy.
```js
// Every option is `true` by default.
var _fp = fp.convert({
  // Specify capping iteratee arguments.
  'cap': true,
  // Specify currying.
  'curry': true,
  // Specify fixed arity.
  'fixed': true,
  // Specify immutable operations.
  'immutable': true,
  // Specify rearranging arguments.
  'rearg': true
});

// The `convert` method is available on each method too.
var mapValuesWithKey = fp.mapValues.convert({ 'cap': false });

// Here’s an example of disabling iteratee argument caps to access the `key` param.
mapValuesWithKey(function(value, key) {
  return key == 'a' ? -1 : value;
})({ 'a': 1, 'b': 1 });
// => { 'a': -1, 'b': 1 }
```

// Manual conversions are also possible with the `convert` module.
```js
var convert = require('lodash/fp/convert');

// Convert by name.
var assign = convert('assign', require('lodash.assign'));

// Convert by object.
var fp = convert({
  'assign': require('lodash.assign'),
  'chunk': require('lodash.chunk')
});

// Convert by `lodash` instance.
var fp = convert(lodash.runInContext());
```