day-48

Array

Initializing an array

const days = new Array();
console.log(days);
// []
const days1 = new Array(5);
days1[2] = 3;
console.log(days1);
// [empty × 2, 3, empty × 2]
const days2 = new Array(1, 2, 3, 4, 5);
console.log(days2);
// [1, 2, 3, 4, 5]
const days3 = [6, 7, 8, 9, 10];
console.log(days3);
console.log(days3.length);
// [6, 7, 8, 9, 10]
// 5

Destructuring arrays

const [x, y] = [1, 2];
console.log(x, y);
// 1 2

Add items to an array with push() and unshift()

const numbers = [3, 4];

numbers.unshift(1, 2);
console.log(numbers);
// [1, 2, 3, 4]
numbers.push(5); 
console.log(numbers);
// [1, 2, 3, 4, 5]

Remove items from an array with pop() and shift()

const items = ['one', 'two', 'three'];

items.pop();
console.log(items);
// ["one", "two"]
items.shift();
console.log(items);
// ["two"]

Remove items using splice()

const array = ['one', 'two', 'three', 'four', 'five'];
array.splice(2, 2);
console.log(array);
// ["one", "two", "five"]

Add items using splice()

const colorChange = (arr, index, newColor) => {
	arr.splice(index, 1, newColor);
	return arr;
} 

let colorScheme = ['#878787', '#a08794', '#bb7e8c', '#c9b6be', '#d1becf'];
colorScheme = colorChange(colorScheme, 2, "#332327");
console.log(colorScheme);
// ["#878787", "#a08794", "#332327", "#c9b6be", "#d1becf"] // #bb7e8c to #332327

Copy an array with slice()

let weatherConditions = ['rain', 'snow', 'sleet', 'hail', 'clear'];
let todaysWeather = weatherConditions.slice(1, 3);
console.log(weatherConditions);
console.log(todaysWeather);
// ["rain", "snow", "sleet", "hail", "clear"]
// ["snow", "sleet"]

Copy an array with spread syntax

const array1 = [true, true, undefined, false, null];
const array2 = [...array1];
console.log(array1);
console.log(array2);
// [true, true, undefined, false, null]
// [true, true, undefined, false, null]

Check for the presence of an element with indexOf()

const fruits = ['apples', 'pears', 'oranges', 'peaches', 'pears'];
console.log(fruits.indexOf('dates')); //  -1
console.log(fruits.indexOf('oranges')); // 2
console.log(fruits.indexOf('pears')); // 1

Iterate through all the items in an array

const example = arr => {
    const newArr = [];
    for (let i = 0; i < arr.length; i++) {
      if (arr[i] > 10) {
        newArr.push(arr[i]);
      }
    }
  return newArr;
}

console.log(example([12, 8, 14, 80, 0]));
// [12, 14, 80]

Create complex nested arrays

// two-dimensional & multidimensional
const nestedArray = [
	['deep'],
	[ 
		['deeper'], ['deeper']
	], 
	[ 
		[ 
			['deepest'], ['deepest']
		], 
		[ 
			[
				['deepest-est?']
			] 
		]
	], 
];

console.log(nestedArray[2][1][0][0][0]);
// deepest-est?

nestedArray[2][1][0][0][0] = 'deeper still';
console.log(nestedArray[2][1][0][0][0]);
// deeper still

Combining arrays with spread syntax

const thisArray = ['three', 'four', 'five'];
const thatArray = ['one', 'two', ...thisArray, 'six'];
console.log(thatArray);
// ["one", "two", "three", "four", "five", "six"]

Object

Initializing an object

const user = new Object();
user.name = 'Nerd';
console.log(user);
// {name: "Nerd"}
const user1 = Object.create(null);
user1['name'] = 'Hemerson';
console.log(user1);
// {name: "Hemerson"}
const name = 'Hemerson'; 
const user2 = {name};
console.log(user2);
// {name: "Hemerson"}
const user3 = {name: 'Item 1', name: 'Item 2'};
console.log(user3);
// {name: "Item 2"}

Destructuring objects

const {name, age} = { name: 'Hemerson', age: 33 };
console.log(name, age);
// Hemerson 33

Use the Delete Keyword to Remove Object Properties

const foods = {
	apples: 10,
	oranges: 2,
	plums: 8,
	bananas: 3
};

delete foods.oranges;
delete foods.plums;
delete foods.bananas;
console.log(foods);
// {apples: 10}

Check if an Object has a Property

const users4 = {
	nerd: {
		age: 33,
		online: true
	}
};

const hasOwnProperty = (prop, obj) => prop in obj ? true : false;
console.log(hasOwnProperty('nerd', users4));
console.log(users4.hasOwnProperty('nerd'));
// true
// true

Iterate Through the Keys of an Object with a for...in Statement

const users5 = {
	nerd: {
		age: 33,
		online: false
	},
	hemerson: {
		age: 43,
		online: true
	},
	calistenico: {
		age: 23,
		online: true
	},
};

const countOnline = obj => { 
	let n = 0;
	for (let user in obj) {
    if (obj[user].online) {
      n++;
    }
  }
	return n;
};

console.log(countOnline(users5));
// 2

Generate an Array of All Object Keys with Object.keys()

const users6 = {
	nerd: {
		age: 33,
		online: false
	},
	hemerson: {
		age: 43,
		online: true
	},
	calistenico: {
		age: 23,
		online: true
	},
};

const getArrayOfUsers = obj => Object.keys(obj);
console.log(getArrayOfUsers(users6));
// ["nerd", "hemerson", "calistenico"]

Modify an Array Stored in an Object

const user = {
	name: 'Nerd',
	age: 33,
	data: {
		username: 'nerd123',
		items: ['book', 'tv']
	}
};

const addItems = (user, item) => {
	user.data.items.push(item);
	return user;
}
console.log(addItems(user, 'computer'));
// { name: 'Nerd', age: 33, data: { username: 'nerd123', items: ['book', 'tv', 'computer'] } }