Functional Programming concept with Javascript (Coding by Composing)

JS Composition is like function husbandry. It’s like combining and mashing multiple functions together to spawn or build a brand new one. As simple as that.

Straight to the example :

var makeUppercase = function(x){
  return x.toUpperCase();
}
var fullStop = function(x){
  return x + '.';
}
var word = compose(makeUppercase, fullStop);
word('hello'); // => 'HELLO.'

Here ‘makeUppercase’ and ‘fullStop’ are two separate function . By using compose function we combined them together and build a new one for an output where we performed two task; Making the ‘word’ uppercase and adding a fullstop at the end.

Mathematical Composition:

In mathematics “f composed with g” is the function that given x, returns f(g(x)). We have to read these from right-to-left . Like first we’ll get ‘the value’ of g(x) then f(‘the value’)!

compose(f, g) --> f(g(x))

Now let’s go through the simplest compose that is used earlier in this tutorial:

var compose = function(f, g) {
   return function(x) {
     return f(g(x));
   };
};