Let's revise on the arrays in JavaScript.

Array Methods and Loops

This is our array.

let colorArray = ["red", "blue", "orange"]

colorArray[0] = "green"

colorArray.push("purple", "black")

colorArray.pop()

colorArray.unshift("white")

colorArray.shift()

let arrayLength = colorArray.length

let colorIndex = colorArray.indexOf("orange")

let colorIndex = colorArray.indexOf("green")

let colorIndex = colorArray.indexOf("gold")

for(let index = 0; index < colorArray.length; index++) {
___console.log(colorArray[index])
}

for(let everyColor of colorArray) {
___console.log(everyColor)
}

for(let index = colorArray.length - 1; index >= 0; index--) {
___console.log(colorArray[index])
}

colorArray.sort()

colorArray.sort().reverse()

An Array of Arrays

This is an array of warm colors.

let warmColors = ["red", "yellow", "orange"]

This is an array of cool colors.

let coolColors = ["green", "blue", "purple"]

This is an array of all colors.

let allColors = [warmColors, coolColors]

Let's display a list of every color in both arrays.

for (let colors of allColors) {
___ for(let color of colors) {
___ console.log(color)
___ }
}

Let's access an element inside of an array of arrays. We need to use 2 pairs of square brackets in order to do that. First pair of brackets is the index of the array we want to access. Second pair is the index of the color within the array.

For example, "blue" is the second color (index 1) in the second array (index 1).

"Red" is the first color (index 0) in the first array (index 0).

"Orange" is the third color (index 2) in the first array (index 0).

Spread Operator (...)

The spread operator will unpack the elements from within our string and array.

Let's use the spread operator on a string.

let myName = "Lena Esposito"

Let's use the spread operator on an array.

let numbers = [1, 2, 3, 4, 5]

Why do we need it? For example, let's find the element with the highest value.
If we use Math.max() without the spread operator, console will print "NaN".

let maximum = Math.max(numbers)

let maximum = Math.max(...numbers)

Rest Parameters (...)

The rest parameter syntax allows a function to accept an indefinite number of arguments as an array.

function sum(...numbers) {
___let total = 0;
___for (const number of numbers) {
___total += number;
___}
___return total;
}

array.forEach()

Let's capitalize the first letter of each element of an array.

let polishCities = ["warsaw", "gdansk", "torun", "lublin", "katowice"]

This function will capitalize the first letter of the elements of the array.

function capitalize(element, index, array){
___array[index] = element[0].toUpperCase() + element.substring(1);
}

This function will print all the capitalized elements in the console.

function list(element) {
___console.log(element)
}

Let's call both functions.

polishCities.forEach(capitalize)
polishCities.forEach(list)

array.map()

Let's map over every element of an array and execute a callback function on it, and therefore, create a new array.

let unfinishedWords = ["coffe", "latt", "cattl", "mous"]

let finishedWords = unfinishedWords.map(addE)

function addE(element) {
___console.log(element + "e")
}

array.filter()

Let's check which elements of an array will pass a test provided by a function, and therefore, create a new array.

let age = [3, 5, 15, 25, 35, 36, 45, 11, 101, 8]

let adults = age.filter(adultsCheck)
adults.forEach(print)

function adultsCheck(arrayElement) {
___return arrayElement >= 18;
}

function print(arrayElement){
___console.log(arrayElement)
}

Sorting an array of numbers in ascending or descending order

let age = [3, 5, 15, 25, 35, 36, 45, 11, 101, 8]

function print(element) {
___console.log(element)
}

Let's sort our array of ages in descending order.

aageDesc = age.sort(ageDescending).forEach(print);

function ageDescending(age1, age2) {
___return age2 - age1;
}

Let's sort our array of ages in ascending order.

ageAsc = age.sort(ageAscending).forEach(print)

function ageAscending(age1, age2) {
___return age1 - age2;
}

array.reduce()

let prices = [3.99, 5.45, 11.99, 104.50]

let total = prices.reduce(addUp)

function addUp(total, element) {
___return total + element
}