Example of JS partial application syntax.

pa-example.js

//A function that returns a function
const adder = a => b => a + b

//Read `adder` left to right as params are passed in, 
//by passing in 5 as `a` we create the function `b => 5 + b`
const add5 = adder(5);

//this is 8
console.log(add5(3));

//you can just chain together arguments without creating intermediate functions
console.log(adder(7)(9));

//this is a function that returns a function that returns a function
const tripleAdder = a => b => c => a + b + c;

//this is a function that returns a function
//is equivalent to `b => c => 7 + b + c`
const doubleAdder7 = tripleAdder(7);

//equivalent to `c => 7 + 1 + c`
const add8 = doubleAdder7(1);

//this is 18
console.log(add8(10));

//this is 6
console.log(tripleAdder(1)(2)(3));