JS Function With Two Parentheses and Two Params

Question

I\'m trying to understand how a function works that is run with two parentheses and two parameters. Like so:

add(10)(10); // returns 20

I k

Answer 1

Welcome to the wonderful world of first order functions

In JavaScript, a function can return a function since a function is just another object. A simple implementation is something like:

function add(x){
    return function addOther(y){
        return x + y;
    };
}

This is possible because of closures and first order functions.

This also lets you do partial application, libraries like Ramda utilize this to great extent.

var addThree = add(3)
addThree(5); // 8