Challenges to iterate over arrays

LoopingOverArrays.md

Challenges

Challeng 1

Create a function which accepts a number as argument and adds 10 to the number.

function addTen(num) {

}

Challenge 2

Use the forEach function to add 10 to each element

let numbers = [10, 20, 30, 40]

Challenge 3

Use the map function to add 10 to each element

let numbers = [10, 20, 30, 40]

Challenge 4

Implement a map function, which takes the array and a callback function which is applied to that array to transform the values. Use the for loop within the map function to iterate over the array.

function map(array, callback) {

}


// console.log(map([1, 2, 3], addTen));

Challenge 5

Implement a forEach function, which iterates over each element and applies the function to each elment.

function forEach(array, callback) {

}


// see for yourself if your forEach works!

Challenge 6

Implement the map function, but instead of using a for loop, now use your custom forEach function to iterate over your array.

function mapWith(array, callback) {

}

Challenge 7

Use the filter function to filter out all the numbers smaller than 30 out of the array.

let numbers = [10, 20, 30, 40]

Challenge 8

Create a function which takes an array and a callback function as arguments. It then filters the array depending on your callback function.

function filter(array, callback) {

}

let numbers = [10, 20, 30, 40]

Challenge 9

Use the reduce function to add up all numbers within the array.

let numbers = [10, 20, 30, 40]

Solution

Challeng 1

function addTen(num) {
	return num + 10
}

Challenge 2

const numbers = [10, 20, 30]


numbers.forEach(function(value, index, array) {
  numbers[index] = numbers[index] + 10
})

console.log(numbers)

Challenge 3

let numbers = [10, 20, 30]

let result = numbers.map(function(value, index, array) {
  return value + 10
})

console.log(result)

Challenge 4

function map(array, callback) {
  let result = []
  for(let i = 0; i < array.length; i++) {
    // callback(item, index, array)  
    let newValue = callback(array[i], i, array)
    result.push(newValue)
  }
  return result
}

map([10, 20, 30], function(value, index, array) {
  return value + 10
});


// console.log(map([1, 2, 3], addTen));

Challenge 5

Implement a forEach function, which iterates over each element and applies the function to each elment.

let numbers = [10, 20, 30, 40]
function forEach(array, callback) {
  for(let index = 0; index < array.length; index++) {
    let value = array[index]
    callback(value, index, array)
  }
}

function addTen(value, index, array) {
  array[index] = value + 10
}

forEach(numbers, addTen)
console.log(numbers1)

Challenge 6

In this challenge we want to use the forEach(array, callback) function to replace the for loop within our map(array, callback) function to create a new map function mapWith(array, callback) which no longer implements an iterative for loop.

function map(array, callback) {
  let result = []
  // Goal is to replace this for loop with
  // a forEach function
  for(let i = 0; i < array.length; i++) {
    let value = array[i]
    let newValue = callback(value, i, array)
    result.push(newValue)
  }
  return result
}

function forEach(array, callback) {
  for (let i = 0; i < array.length; i++) {
    let value = array[i];
    callback(value, i, array);
  }
}

function mapWith(array, callback) {
  let result = []
  forEach(array, function (value, index, array) {
    let newValue = callback(value, index, array)
    result.push(newValue)
  })
  return result
}

let array1 = [10, 20, 30, 40];
mapWith(array1, function(value) {
  return value + 20
});

Gracias Dominik!