A library designed specifically for a functional programming style, one that makes it easy to create functional pipelines, one that never mutates user data.

ramda

Learn how you can use ramda.js to bring functional programming concepts into your JavaScript code. Ramda offers composability and immutability right out of the box, so you can leave your imperative code behind and build cleaner, more maintainable code.

In this lesson we'll take some existing code and refactor it using some functions from the Ramda library, most notably, `compose` and `converge`. When we're done, we'll have taken a function with a couple of local variables and parameter references and converted it into more streamlined "point-free" or "tacit" functions.

Refactor to Point Free Functions with Ramda using compose and converge

In this lesson we'll use a handful of Ramda's utility functions to take a queryString full of name/value pairs and covert it into a JavaScript object so we can access those properties in a more useful way. Along the way, we'll build up a composition and look at the `tail`, `split`, `map` and `fromPairs` functions, along with the crucial `compose` function.

Convert a QueryString to an Object using Function Composition in Ramda

In this lesson we'll take an array of objects and map it to a new array where each object is a subset of the original. We'll look at multiple ways to accomplish this, refactoring our code into a simple and easy to read function using Ramda's `map`, `pick` and `project` functions.

Select a Subset of Properties from a Collection of Objects in Ramda

When you want to build your logic with small, composable functions you need a functional way to handle conditional logic. You _could_ wrap ternary expressions and if/else statements in functions, handling all of the concerns around data mutation yourself, or you could leverage the conditional functions supplied by Ramda. In this lesson, we'll cover several of Ramda's conditional functions: `ifElse`, `unless`, `when` and `cond`

Handle Branching  Logic with Ramda's Conditional Functions

Sometimes you need to filter an array of objects or perform other conditional logic based on a combination of factors. Ramda's `where` function gives you a concise way to declaratively map individual predicates to object properties, that when combined, cover the various facets of your conditions. In this lesson, we'll look at how this powerful function can be used for scenarios requiring a complex predicate function.

Declaratively Map Predicates to Object Properties Using Ramda where

In this lesson we'll learn the basics of using lenses in Ramda and see how they enable you to focus changes on specific properties of an object while keeping your data immutable. 

Change Object Properties with Ramda Lenses

We'll learn how to get a subset of an array by specifying items to include with filter, or items to exclude using reject. We'll also look at how to get the results from both filter and reject, neatly separated with partition.

Add and Remove Items in Arrays using Filter, Reject and Partition in Ramda

We'll learn how to take advantage of Ramda's automatic function currying and data-last argument order to combine a series of pure functions into a left-to-right composition, or pipeline, with Ramda's pipe function.

Build a Functional Pipeline with Ramda.js

Sometimes you just need a subset of an object. In this lesson, we'll cover how you can accomplish this using Ramda's pick and omit functions, as well as the pickAll and pickBy variants of pick. 

Pick and Omit Properties from Objects Using Ramda

Most of the functions offered by the ramda library are curried by default. Functions you've created or that you've pulled in from another library may not be curried. Ramda's `curry` and `curryN` functions allow you to take a non-curried function and use it as a curried functions. In the case where you have a manually curried function and you want to just call it like a normal function, you can use `uncurryN` to get back a function that accepts all of the arguments at once.

Curry and Uncurry Functions with Ramda

We don't always control the data we need in our applications, and that means we often find ourselves massaging and transforming our data. In this lesson, we'll learn how to transform objects in a declarative way using ramda's evolve function.

Declaratively Map Data Transformations to Object Properties Using Ramda evolve

Handling your logic with composable functions makes your code declarative, leading to code that's easy to read and easy to test. Breaking that up to wrap some risky function in a `try/catch` block introduces imperative code and makes it harder to maintain that declarative approach. With Ramda's `tryCatch` function, you can handle errors right in the middle of a composition and leave your code clean and functional. We'll also see how you can use `propOr` to avoid common "cannot find X of undefined" errors.

Handle Errors in Ramda Pipelines with tryCatch

In this lesson we'll look at how you can use Ramda's `unfold` function to generate a list of values based on an initial seed.

Create an Array From a Seed Value with Ramda's unfold

In this lesson, we'll use `Promise.all` to get an array that contains the resolved values from multiple promises. Then we'll see how we can use Ramda to convert that array of values into a single object using `zip` with `fromPairs`. Then we'll refactor to use `zipObj`.

Convert a Promise.all Result to an Object with Ramda's zip and zipObj

In this lesson, we'll filter a list of objects based on multiple conditions and we'll use Ramda's `allPass` function to create a joint predicate from multiple, individual predicate functions.

Filter an Array Based on Multiple Predicates with Ramda's allPass Function

In this lesson, we'll use Ramda's `toPairs` function, along with `map`, `join`, `concat` and `compose` to create a reusable function that will convert an object to a querystring.

Create a Query String from an Object using Ramda's toPairs function

In this lesson, we'll look at how we can use Ramda's `invoker` and `constructN` functions to take methods of an object and turn them into reusable utility functions that are curried and accept their object as the last argument. We'll convert a dot-chained string of jQuery methods and create a composed function that can be applied to multiple elements.

Convert Object Methods into Composable Functions with Ramda

Sorting an array of objects by multiple fields can be tricky. Even worse, the code can be tough to follow and making changes in the future is complicated by conditional logic in the sorting function. In this lesson we'll see how to simplify this using Ramda's `sortWith` along with `ascending` and `descending`. We'll sort an array of objects by multiple fields and the code will be readable and dead simple to change.

Sort an Array of Objects by Multiple Fields with Ramda's sortWith

Promise chains can be a powerful way to handle a series of transformations to the results of an async call. In some cases, additional promises are required along the way. In cases where there are no new promises, function composition can reduce the number of dot chained `then`s you need. In this lesson, we'll look at how to take a promise chain, and reduce it down with function composition.

Refactor a Promise Chain to Function Composition using Ramda

Naming things is hard and arguments in generic utility functions are no exception. Making functions "tacit" or "point free" removes the need for the extra parameter names and can make your code cleaner and more succinct. In this lesson, we'll create a normal, "pointed" function and then use ramda's `useWith` function to refactor our way to point-free bliss.

Refactor to a Point Free Function with Ramda's useWith Function

In this lesson, we'll grab arrays of values from other arrays, resulting in a nested array. From there, we'll look at multiple ways to flatten the array structure using composition with `map` and `unnest` and then refactoring to use `chain`, AKA `flatMap`. Finally, we'll add Ramda's `uniq` function to remove duplicate values.

Get a List of Unique Values From Nested Arrays with Ramda

Functional composition is a great way to write declarative code that reads well. But sometimes, you need to get insight into what's happening at different steps in your composition. This is where `tap` comes in. With tap, we can run code that generates side-effects, like logging to the console, and our data will continue to be passed along, untouched.

Debug Function Compositions with Ramda's Tap Function

Using the map method of an array is a great way to create new data from an existing array in an immutable way and without writing any loops. The problem is that you need to call it on an existing array instance. In the lesson we'll see how to build our own reusable `map` utility function using manual currying and then we'll replace it with Ramda's `map`.

Create a Reusable Mapping Function with Ramda's Map

In this lesson we'll see how Ramda's `path` and `pathOr` functions can be used to safely access a deeply nested property from an object while avoiding the dreaded checks for `undefined` at each new property in the desired path. 

Get Deeply Nested Properties Safely with Ramda's path and pathOr Functions

In this lesson we'll see how to use the `without` function to remove items in a known list from an array. Then we'll generate our exclusion list and apply it to `without` using `reduce`, `min`, `max` and `converge` to detect the highest and lowest values in an array and creating a new array that excludes those values.

Functional Programming in JavaScript with Ramda.js

Andy Van Slaars

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