A simple example of currying in JS

curry.js

// This is a 'curried' function. If it receives less params than it expects, it returns a function which expects the rest of the params.
function add(a, b) {
  // if 2nd param wasn't passed, return a function that holds the 1st param via closure, but expects another param.
  if (typeof b === "undefined") {
    return function(c) {
      a + c;
    }
  }
  
  // if 2 params are passed return the result
  return a + b;
}

add(2,2);
// 4

// we are now using the curried function
add(1)(2);
// 3

// and we can do this...
var add2 = add(2);
add2(3); 
// 5

// some more reading here:
// https://javascriptweblog.wordpress.com/2010/04/05/curry-cooking-up-tastier-functions/