Learning Functional Programming with JS

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

OK, let’s do it!

...how?

Do everything with functions

input -> output

Not functional:

var name = “Lakshya”;
var greeting = “Hi, I’m ”;
console.log(greeting + name);
=> “Hi, I’m Lakshya”

Functional:

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

Avoid side effects

use “pure” functions

Not pure:

var name = “Lakshya”;
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(“dev”);
coolifier(“to”);
  => “dev to”

Don’t iterate

use map, reduce, filter

Source: https://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"]