## 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.
+The `lodash/fp` module promotes a more
+[functional programming](https://en.wikipedia.org/wiki/Functional_programming)
+(FP) friendly style by exporting 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>
+<script src='https://cdn.jsdelivr.net/g/lodash@4(lodash.min.js+lodash.fp.min.js)'></script>
+<script>
+// Loading `lodash.fp.js` converts `_` to its fp variant.
+_.defaults({ 'a': 2, 'b': 2 })({ 'a': 1 });
+// ➜ { 'a': 1, 'b': 2 }
+
+// Use `noConflict` to restore the pre-fp variant.
+var fp = _.noConflict();
+
+_.defaults({ 'a': 1 }, { 'a': 2, 'b': 2 });
+// ➜ { 'a': 1, 'b': 2 }
+fp.defaults({ 'a': 2, 'b': 2 })({ 'a': 1 });
+// ➜ { 'a': 1, 'b': 2 }
+</script>
```
In Node.js:
```js
// Load the fp build.
-var _ = require('lodash/fp');
+var fp = require('lodash/fp');
// Load a method category.
var object = require('lodash/fp/object');
var extend = require('lodash/fp/extend');
```
-## Convert
+## Mapping
-Although `lodash/fp` & its method modules come pre-converted there are times when
-you may want to convert another lodash package or create a customized conversion.
-That’s when the `convert` module comes in handy.
+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.
-```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());
-```
+#### Capped Iteratee Arguments
-It’s even customizable.
+Iteratee arguments are capped to avoid gotchas with variadic iteratees.
```js
-// Every option is `true` by default.
-var filter = convert('filter', _.filter, {
- // 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
-});
-
-// Specify `cap` of `false` to create a function that doesn’t cap iteratee arguments.
-var filter = convert('filter', _.filter, { 'cap': false });
-
-filter(function(value, index) {
- return index % 2 == 0;
-})(['a', 'b', 'c']);
-// => ['a', 'c']
+// The `lodash/map` iteratee receives 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]
```
-## Mapping
-
-Immutable auto-curried iteratee-first data-last methods sound great, but what’s
-that really mean for each method? Below is a breakdown of the mapping used to
-convert each method.
-
-#### Capped Iteratee Arguments
-
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)
+The iteratee of `mapKeys` is capped to one argument: `(key)`
#### Fixed Arity
+Methods have fixed arities to support auto-currying.
+```js
+// `lodash/padStart` accepts an optional `chars` param.
+_.padStart('a', 3, '-')
+// ➜ '--a'
+
+// `lodash/fp/padStart` does not.
+fp.padStart(3)('a');
+// ➜ ' a'
+fp.padCharsStart('-')(3)('a');
+// ➜ '--a'
+```
+
Methods with a fixed arity of one:<br>
-<%= toFuncList(mapping.aryMethod[1]) %>
+<%= toFuncList(_.difference(mapping.aryMethod[1], _.keys(mapping.skipFixed))) %>
Methods with a fixed arity of two:<br>
-<%= toFuncList(mapping.aryMethod[2]) %>
+<%= toFuncList(_.difference(mapping.aryMethod[2], _.keys(mapping.skipFixed))) %>
Methods with a fixed arity of three:<br>
-<%= toFuncList(mapping.aryMethod[3]) %>
+<%= toFuncList(_.difference(mapping.aryMethod[3], _.keys(mapping.skipFixed))) %>
Methods with a fixed arity of four:<br>
-<%= toFuncList(mapping.aryMethod[4]) %>
+<%= toFuncList(_.difference(mapping.aryMethod[4], _.keys(mapping.skipFixed))) %>
#### Rearranged Arguments
-Methods with a fixed arity of two have an argument order of:<br>
+Method arguments are rearranged to make composition easier.
+```js
+// `lodash/filter` is data-first iteratee-last:
+// (collection, iteratee)
+var compact = _.partial(_.filter, _, Boolean);
+compact(['a', null, 'c']);
+// ➜ ['a', 'c']
+
+// `lodash/fp/filter` is iteratee-first data-last:
+// (iteratee, collection)
+var compact = fp.filter(Boolean);
+compact(['a', null, 'c']);
+// ➜ ['a', 'c']
+```
+
+##### Most methods follow these rules
+
+A fixed arity of two has an argument order of:<br>
<%= toArgOrder(mapping.aryRearg[2]) %>
-Methods with a fixed arity of three have an argument order of:<br>
+A fixed arity of three has an argument order of:<br>
<%= toArgOrder(mapping.aryRearg[3]) %>
-Methods with a fixed arity of four have an argument order of:<br>
+A fixed arity of four has 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') %>
+##### Exceptions to the rules
+
+Methods that accept an array as their last or only argument:<br>
+<%= toFuncList(_.keys(mapping.methodSpread)) %>
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.
+Methods with custom argument orders:<br>
+<%= _.map(_.keys(mapping.methodRearg), methodName => {
+ const orders = mapping.methodRearg[methodName];
+ return ' * `_.' + methodName + '` has an order of ' + toArgOrder(orders);
+}).join('\n') %>
+
+The iteratee of `reduceRight` has an argument order of: `(b, a)`
#### 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 ' * Added `_.' + alias + '` as an alias of `_.' + realName + '`';
+<%= _.map(_.keys(mapping.aliasToReal).sort(), alias => {
+ const realName = mapping.aliasToReal[alias];
+ return ' * `_.' + alias + '` is an alias of `_.' + realName + '`';
}).join('\n') %>
+
+## Placeholders
+
+The placeholder argument, which defaults to `_`, may be used to fill in method
+arguments in a different order. Placeholders are filled by the first available
+arguments of the curried returned function.
+```js
+// The equivalent of `2 > 5`.
+_.gt(2)(5);
+// ➜ false
+
+// The equivalent of `_.gt(5, 2)` or `5 > 2`.
+_.gt(_, 2)(5);
+// ➜ true
+```
+
+## 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)
+on using functional composition as an alternative to method chaining.
+
+## 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());
+```
+
+## Tooling
+
+Use [eslint-plugin-lodash-fp](https://www.npmjs.com/package/eslint-plugin-lodash-fp)
+to help use `lodash/fp` more efficiently.
git://repos.xcallymotion.com / motion.git / blobdiff