index.js

// what is a callback function in js?

[1, 2, 3].forEach((v, i) => {
  console.log(v)
})

const myFunc = (cb) => {
  return cb(10)
}

const result1 = myFunc((num) => {
  return num * 10
})

console.log(result1)
// => 100

function adder1(x, y, callback) {
  let answer = x + y;
  // => 3

  if (callback) {
    return callback(answer);
  }

  return answer;
}

function shoutSomething(answer) {
  return answer
}

const result2 = adder1(1, 2, shoutSomething);
console.log(result2)
// => 3

const invokeCallback = (cb) => {
  console.log('2')
  const result = cb(10)
  // => 100
  console.log('4')
  return result
}

const adder2 = (number) => {
  console.log('3')
  return number * number
  // => 100
}

console.log('1')
console.log(invokeCallback(adder2))
console.log('5')
// => 100

// ---

const arr = [1,2,3]
// own custom forEach
// yield

Array.prototype.myForEach = function(cb) {
  // .forEach
  // what does forEach do?
  // while
  const len = this.length
  let index = 0
  while(index < len) {
    cb(this[index], index)
    index += 1
  }
  console.log("###")
}

// custom to me
arr.myForEach((item, index) => {
  console.log(`The item is ${item}`)
  console.log(`The index is ${index}`)
  console.log(`------`);
})

// built into the language
arr.forEach((item, index) => {
  console.log(`The item is ${item}`)
  console.log(`The index is ${index}`)
  console.log(`------`);
})