Basic Data Structures

Question 1

What Are Basic data structures in Javascript ?

Answer 1

Variable, Arrays and Objects

Question 2

How to add item at the beginning of an array ?

Answer 2

let arr = [1,2,3,4];

arr.unshift(0);

//result 0,1,2,3,4

Obs.: unshift method accepts one or more parameters

Question 3

How to add item at the end of an array ?

Answer 3

let arr = [0 ,1,2,3,4];

arr.push(5);

//result 0,1,2,3,4,5

Obs.: push method accepts one or more parameters

Question 4

How to remove item at the beginning of an array ?

Answer 4

let arr = [0,1,2,3,4,5];

arr.shift();

//result 1,2,3,4,5

Obs.: doens’t accepts parameters
Obs.: returns element removed

Question 5

How to remove item at the end of an array ?

Answer 5

let arr = [0,1,2,3,4,5];

arr.pop();

//result 0,1,2,3,4

Obs.: doens’t accepts parameters
Obs.: returns element removed

Question 6

How to remove itens at the middle of an array ?

Answer 6

let arr = [2, 5, 1, 5, 2, 1];
  let removed = arr.splice(2, 2);

 // sum elements
  arr.reduce((a, b) => a + b);

//result 10

Obs.: returns an array with elements removed

Question 7

How to change values of an array using splice ?

Answer 7

let arr = [“eu”, “gosto”, “de”, “praia”];

arr.splice(3, 1, “parque”);

//results [“eu”, “gosto”, “de”, “parque”]

Question 8

How to retrieve a slice of an array ?

Answer 8

let animals = [“dog”, “cat”, “giraffe”, “crocodile”, “elephant”];

let pets = animals .slice(0,2);

//results pets ==> ["dog","cat"]
// results ==> animals ["dog", "cat", "giraffe", "crocodile", "elephant"]

Obs.: slice doesn’t change the source array.

Question 9

How to copy an entire array without ref and without change it?

Answer 9

let jsDataTypes = [‘boolean’,’undefined’,’number’, ‘null’,’string’, ‘symbol’];

let data = […jsDataTypes];

//results data ==> [‘boolean’,’undefined’,’number’, ‘null’,’string’, ‘symbol’]

Question 10

How to Combine Arrays with the Spread Operator ?

Answer 10

let japanCarBrand = [‘toyota’,’honda’,’nissan’];
let usaCarBrand = [‘ford’, ‘chevrolet’,’GMC’];
let franceCarBrand = [‘renault’, ‘citroen’,’pegeout’];

let carBrands = […japanCarBrand, …usaCarBrand, …franceCarBrand];

//results [‘toyota’,’honda’,’nissan’,’ford’, ‘chevrolet’,’GMC’,’renault’, ‘citroen’,’pegeout’]

Question 11

How to check if an alement exists in the array ?

Answer 11

let names = [‘sandra’, ‘julia’, ‘meryl’, ‘angelina’,’scarlet’];

let index = names.indexOf(‘julia’);

//results 1

Question 12

How to through all itens of an array with basic for loop ?

Answer 12

let decades = [1970,1980,1990,2000,2010];

for (let i = 0; i < decades.length; i++){
    console.log(decades[i]);
}
//results 1970, 1980, 1990, 2000, 2010

Question 13

How to create complex multi-dimensional arrays ?

Answer 13

let myNestedArray = [
  // change code below this line
  [
    [
      'terceiro nível',
      [
        'quarto nível',
        [
          'quinto nível',
          'deepest'
        ],
        'deeper'
      ],
      'deep'
    ]
  ]
];

console.log(myNestedArray[0][0][1][1][1]);
//results deepest

Question 14

How to create an object in Javascript ?

Answer 14

let foods = {
  apples: 25,
  oranges: 32,
  plums: 28
};

Question 15

How to add properties to an existing object ?

Answer 15

let foods = {
  apples: 25,
  oranges: 32,
  plums: 28
};

//add new properties

foods. bananas = 13;
foods. grapes = 35;
foods. strawberries = 27;

Obs.: If the property doesn’t exist yet, is created with the value passed;

Question 16

How to Modify an Object Nested Within an Object ?

Answer 16

let userActivity = {
  id: 23894201352,
  date: 'January 1, 2017',
  data: {
    totalUsers: 51,
    online: 42
  }
};
userActivity.data.online = 45;

Question 17

How to retrieve value from object property accessing by variable ?

Answer 17

let foods = {
  apples: 25,
  oranges: 32,
  plums: 28,
  bananas: 13,
  grapes: 35,
  strawberries: 27
};

function checkInventory(scannedItem) {
  // change code below this line
return foods[scannedItem];
}

// returns 25

Question 18

How to remove a property from object ?

Answer 18

let foods = {
  apples: 25,
  oranges: 32,
  plums: 28,
  bananas: 13,
  grapes: 35,
  strawberries: 27
};

delete foods.oranges;
delete foods.plums;
delete foods.strawberries;

Question 19

How to check if an object has a property ?

Answer 19

let users = {
  Alan: {
    age: 27,
    online: true
  },
  Jeff: {
    age: 32,
    online: true
  },
  Sarah: {
    age: 48,
    online: true
  },
  Ryan: {
    age: 19,
    online: true
  }
};

//using 'in'
function isEveryoneHere(obj) {
return 'Alan', 'Jeff', 'Sarah', 'Ryan' in obj;
}
// results true

or alternatively

//using 'hasOwnProperty'
function isEveryoneHere(obj) {
 return obj.hasOwnProperty('Alan');
}

//returns true

Question 20

How to Iterate Through the Keys of an Object ?

Answer 20

Possible Solution

let users = {
  Alan: {
    age: 27,
    online: false
  },
  Jeff: {
    age: 32,
    online: true
  },
  Sarah: {
    age: 48,
    online: false
  },
  Ryan: {
    age: 19,
    online: true
  }
};

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

console.log(countOnline(users));

// results 2

Note: for … in statement brings only the object key. To access the property value it is necessary to pass the object key to retrieve the value of the object.

Question 21

How to all keys from a object ?

Answer 21

let users = {
  Alan: {
    age: 27,
    online: false
  },
  Jeff: {
    age: 32,
    online: true
  },
  Sarah: {
    age: 48,
    online: false
  },
  Ryan: {
    age: 19,
    online: true
  }
};

Object.keys(users);

//results Alan,Jeff,Sarah,Ryan

Question 22

How to add item in the array wihthin object property ?

Answer 22

let user = {
  name: 'Kenneth',
  age: 28,
  data: {
    username: 'kennethCodesAllDay',
    joinDate: 'March 26, 2016',
    organization: 'freeCodeCamp',
    friends: [
      'Sam',
      'Kira',
      'Tomo'
    ],
    location: {
      city: 'San Francisco',
      state: 'CA',
      country: 'USA'
    }
  }
};

function addFriend(userObj, friend) {
  userObj.data.friends.push(friend);
  return userObj.data.friends;
}

console.log(addFriend(user, ‘Pete’));

//Results Sam,Kira,Tomo,Pete