JavaScript and Functional Programming

https://bethallchurch.github.io/JavaScript-and-Functional-Programming/

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var add = (x, y) => x + y

var square = (x) => x * x

var addThenSquare = (x, y) => square(add(x, y))

addThenSquare(5, 2)

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var composeTwo = (f, g) => (x, y) => g(f(x, y))

var addThenSquare = composeTwo(add, square)

addThenSquare(5, 2)

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var composeMany = (...args) => {
  var funcs = args;
  return (...args) => {
    funcs.forEach(func => {
      args = [func.apply(this, args)];
    });
    return args[0]
  }
}

var addThenSquare = composeMany(add, square)

addThenSquare(5, 2)

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var multiply = (x, y) => x * y

var partApply = (fn, x) => (y) => fn(x, y)

var double = partApply(multiply, 2)
var triple = partApply(multiply, 3)
var quadruple = partApply(multiply, 4)

console.log(double(2))
console.log(triple(2))
console.log(quadruple(2))

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var multiply = (x, y) => x * y

var curry = fn => x => y => fn(x, y) // is a function that takes `fn` as an argument and returns function `x => y => fn(x, y)`

var curriedMultiply = curry(multiply) // is a function returned from `curry` that takes `x` as an argument and returns function `y => multiply(x, y)`

var double = curriedMultiply(2) // is a function returned from `curriedMultiply` that takes `y` as an argument and calls `multiply(2, y)`

console.log(double(3))
console.log(`is same as multiply(2, 3)`:, multiply(2, 3))

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var multiply = (x, y, z) => x * y * z

var curry = fn => x => y => z => fn(x, y, z)

var partApply = (fn, x) => (y, z) => fn(x, y, z)

var curriedMultiply = curry(multiply)
var partiallyAppliedMultiply = partApply(multiply, 10)

console.log(curriedMultiply(10)(5)(2));
console.log(partiallyAppliedMultiply(5, 2));

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var factorial = n => n === 0 ? 1 : n * factorial(n - 1)

console.log(factorial(10))

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var factorial = (n, base) => {
  if (n === 0) {
    return base;
  }
  base *= n;
  return factorial(n - 1, base)
}

console.log(factorial(10, 1))