Mastering JavaScript Callbacks!

General limitations

• Read this first http://eloquentjavascript.net/05_higher_order.html

1. You are not allowed to change input variable of a any function.
2. You are allowed to use only 'const' for declaring variables and functions.
3. You are not allowed to use any of ++ or -- operators.
4. You are not allowed to use 'delete' operator
5. You are not allowed to use .shift, .splice, .push or any function that mutates an array in place.
6. You cannot mutate and created object. example: const a = {key: 1}; a.key = 123

• First write without limitations, then refactor code to match limitations

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1. Write a function that accepts another function as an argument and call that function passing a number

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2. Assume you have function

const giveRand = callback => {
  callback(Math.random())
}

TASK

Write a function that calls function 'giveRand' 10 times and averages the results.

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3. Assume you have a function and an array

const f = (argument, callback) => {
  if (argument === 4) {
    callback(false)
    return
  }
  callback(true)
}

const array = [2, 3, 4, 5, 6, 7, 8]

TASK

Write a function that calls function 'f' for each element of an array, starting from the first one, and if callback receives 'true', stop calling 'f'

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Async Callbacks, setTimeout, setInterval

4. Assume you have an async function and an array

const giveTrueIf4Async = (arg, callback) => {
  const result = arg === 4
  const f = () => callback(result)
  setTimeout(f, 10)
}
const array = [2, 3, 4, 5, 6, 7, 8]

TASK

Write a function that calls function 'giveTrueIf4Async' for each element of an array, one at a time, starting from the first one, and if callback receives 'true', stop calling 'giveTrueIf4Async'

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5. Assume you have async function, that give random numbers to callback

const giveRandAsync = callback => {
  const f = () => callback(Math.random())
  setTimeout(f, 10)
}

TASK

• Call function 'giveRandAsync' 10 times and gather results in an array
• Call function 'giveRandAsync' 10 times, one at a time, and average the results
• Call function 'giveRandAsync' 10 times, one at a time with 20 second interval, and average the results
• Call function 'giveRandAsync' 10 times, all at once, and average the results

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Super Dudes

Array.push is allowed here

TASK

Write your own implementation of async.waterfall function Write your own implementation of async.parallel function

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Promises

TASK

• Write your own implementation of bluebird's functions.
• Promise.map
• Promise.all
• Promise.each
• Promise.tap
• Promise.thenReturn