Functionnal programming

Learning Functional
Programming with JS
@RajohnsonAndry

What is functional programming?

a programming paradigm

a coding style

a mindset

a sexy, buzz-wordy trend

Why functional JavaScript?
object-oriented JS gets tricky
(prototypes? this?!?)

safer, easier to debug/maintain

established community

Do everything with functions
input -> output

Not functional:
var name = “Andry”;
var greeting = “Hi, I’m ”;
console.log(greeting + name);
=> “Hi, I’m Andry”

Functional:
function greet(name) {
return “Hi, I’m ” + name;
}
greet(“Andry”);
=> “Hi, I’m Andry”

Avoid side effects
use “pure” functions

Not pure:
var name = “Andry”;
function greet() {
console.log(“Hi, I’m ” + name);
}

Pure:
function greet(name) { return
“Hi, I’m ” + name;
}

Use higher-order functions
functions can be inputs/outputs

function makeAdjectifier(adjective) {
return function (string) {
return adjective + “ ” + string;
};
}
var coolifier = makeAdjectifier(“cool”);
coolifier(“conference”);
=> “cool conference”

Don’t iterate
use map, reduce, filter

http://www.datasciencecentral.com/forum/topics/what-is-map-reduce

Avoid mutability
use immutable data

Mutation (bad!):
var rooms = [“H1”, “H2”, “H3”];
rooms[2] = “H4”;
rooms;
=> ["H1", "H2", "H4"]

No mutation (good!):
var rooms = [“H1”, “H2”, “H3”];
var newRooms = rooms.map(function (rm) { if (rm
== “H3”) { return “H4”; }
else { return rm; }
});
newRooms; => ["H1", "H2", "H4"]
rooms; => ["H1", "H2", "H3"]

Persistent data structures
for efficient immutability
Mori, Immutable.js

FP libraries for JS
 Mori (http://swannodette.github.io/mori/)
 Immutable.js (https://facebook.github.
io/immutable-js/)
 Underscore (http://underscorejs.org/)
 Lodash (https://lodash.com/)
 Ramda (http://ramdajs.com/)
 ...and more!

“An introduction to functional
programming”
by Mary Rose Cook
https://codewords.recurse.com/issues/one/an-introduction-to-functional-programming

Thanks for listening!
I’m @RajohnsonAndry

Functionnal programming

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