Functional Programming in JavaScript Chapter 01 - run function

ch01-magic-run.js

/*
 * Functional Programming in JavaScript
 * Chapter 01
 * Magical -run- function in support of Listing 1.1
 * Author: Luis Atencio
 */
// -run- with two functions 
var run2 = function(f, g) {
    return function(x) {
        return f(g(x));
    };
};

// -run- with three functions
var run3 = function(f, g, h) {
    return function(x) {
          return f(g(h(x))); 
    };
};

// Test this magical function
var add1 = function(x) {return x + 1;};
var mult2 = function(x) {return x * 2;};
var square = function(x) {return x * x;};
var negate = function(x) {return -x;};

var double = run2(add1, add1);
console.log(double(2)); //-> 4

var testRun = run3(negate, square, mult2);
console.log(testRun(2)); //->-16

In Listing 1.4, the curry is not given, So I found this code below

const curry = function(f) {
    const var_num = f.length
    return function(...args) {
      if (args.length >= var_num) {
        return f.apply(null, args)
      }
      return function(...new_args) {
        return f.apply(null, args.concat(new_args))
      }
    }
  }

Hope I can help someone who is a beginner like me, good luck!