JavaScript exercises - Basics

1. Create 3 empty arrays e1, e2, e3, in 3 different ways.
2. Create 2 arrays a1 and a2, containing a single element 1, in 2 different ways.

const a = [1, 2, 3, 4, 5];

Create 3 arrays a1, a2 and a3 in 3 different ways so that they contain the same elements as a and so that they are independent from one another. Mutating the array a should not mutate any of the 3 other arrays.

let letters = [...'Elephant'];

Iterate through the letters array to display each letter to the screen. Do it in 5 different ways.

const numbers_1 = [1, 2, 3];
const numbers_2 = [4, 5, 6];

Concatenate the 2 arrays numbers_1 and numbers_2 and assign the result to a new variable called numbers.

const numbers = [0, 1, 2, 3, 4, 5];

Create 3 new arrays doubled_1, doubled_2, doubled_3 that have doubled values compared to numbers. Use 4 different ways to do so.

const a = [5, 4, 3, 2, 1];

Create a new array b that contains the values from a that are even.

const a = [1, 2, 3, 4, 5];

Find the 1st element in a that is greater or equal to 3 and assign the value to a new variable b.

const a = [1, 2, 3, 4, 5];

Find the index of the 1st element that is even and assign the value to a new variable b.

const a = [1, 2, 3, 4, 5];

Check if all values of a are greater or equal to 10 and store the resulting value into a new variable all.

const numbers = [0, 1, 2, 3, 4, 5];
const words = ['Pizza', 'Cheesy Cannelloni', 'Osso buco'];

1. Use the method reduce() to calculate the sum of all values contained in the array numbers. Assign the result to a new variable sum.
2. Use the method reduce() to find the longest word in the array words. Assign the result to a new variable longest.

const numbers = [0, 1, 2, 3, 4, 5];

Create a new array selected that contains all values of numbers from index 1 to index 3.

const numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

Delete the values 2 and 3 in numbers and replace them with 'a' and 'b'.

const numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

Delete all values from numbers, starting at index 4. numbers should only contain the values of indices 0, 1, 2 and 3.

const a = [1, 2, 3, 4, 5];

Check if any value of a is negative and store the resulting value into a new variable any.

1. Declare a constuctor function named Cat(), that can set the properties _age and _name of any instance of a cat.
2. Add a function jump() that can be common to all cat instances. Do not modify the code of the Cat()constructor function you already declared. The jump() method should log the string 'Fiuuuuu!'.
3. Create a cat felix named 'Felix' and aged 3.
4. Create a cat tom named 'Tom' and aged 5.
5. Add a getter method for getting any cat name. The getter should be defined in the prototype of Cat.
6. Use the getter function to print to the screen the names of felix an tom in 2 separate statements.

1. Use a factory function to create a class of dogs that have a _name, an _age and that can bark. The bark() method should display the string 'Woof!'.
2. Create a dog toby named 'Toby' and aged 2.
3. Create a dog fox named 'Fox' and aged 4.
4. Display the names of the dogs by using a getter method.

1. Declare a constructor function named Rabbit, with the keyword class to create a class of rabbits that have a _name, an _age and that can eat. The eat() method should log the string 'Crr crr crr'. The class should also have a getter method name to get the _name of a rabbit.
2. Create a rabbit bugs named 'Bugs' and aged 1.
3. Create a rabbit Roger named 'Roger' and aged 3.
4. Display the names of the rabbits by using a getter method.

const light = 'green';
let action = '';

if (light === 'green') {
  action = 'Go';
} else if (light === 'yellow') {
  action = 'Slow down';
} else if (light === 'red') {
  action = 'Stop';
} else if (light === 'blue') {
  action = 'Pull over';
} else {
  action = 'Look at the sky';
}

Rewrite the previous code by using a switch statement.

const light = 'green';
let action = '';

if (light === 'green') {
  action = 'Go';
} else {
  action = 'Stay still';
}

Rewrite the previous code by using the ternary operator.

let a;
if (a) {
  console.log('a');
}

let b = a;

if (b = {}) {
  console.log('b'); 
}

let c = [''];

if (!c) {
  console.log('c');
}

if (!c[0]) {
  console.log('d');
}

if (0) {
  console.log('e');
}

What does the previous code display to the screen?

const text = 'Elephant';

Convert the variable text into a Boolean and store the new value into a another variable called bool.

Display to the screen the value of bool.

const text = '3.1415';

Convert variable text into a number and store the new value into another variable called num.

const bool = true;

Convert the variable bool into a String and store the new value into another variable called text.

const num = 10;

Convert the variable num into a String and store the new value into another variable called text.

const num = 3.1415;

Convert the variable num into a String that represents the value with only 2 digits after the decimal point. Store the new value to another variable called text.

const text = '22';

Convert variable text into a number and store the new value into another variable called num.

Define 3 functions f1, f2 and f3 that have 1 parameter text and that display text to the screen. Use 3 different ways to do it.

Create an arrow function basic() that simply returns the object { a: 1 }.

Define a function print that can take an undefined number of arguments, and that logs each argument to the console.

const singSong_1 = (song) => {
  console.log(`This song "${song}" is great!`);
};

const singSong_2 = (song = 'Billy Jean') => {
  console.log(`This song "${song}" is great!`);
};

singSong_1();
singSong_2();

What does the previous code display to the screen?

// file-1.js
const sum = (x, y) => x + y;
const square = x => x * x;
const mean = data => data.reduce(sum) / data.length;

Export the function sum by using the native node.js syntax (also known as the CommonJS syntax).

// file-1.js
const sum = (x, y) => x + y;
const square = x => x * x;
const mean = data => data.reduce(sum) / data.length;

Export the functions sum and square by using the native node.js syntax (also known as the CommonJS syntax).

// file-1.js
const sum = (x, y) => x + y;
const square = x => x * x;
const mean = data => data.reduce(sum) / data.length;

module.exports = { sum, square };

Let us assume that there is a file file-2.js in the same directory as file-1.js. Import the function sum from file-1.js into file-2.js by using the native node.js syntax (also known as the CommonJS syntax).

// file-1.js
const sum = (x, y) => x + y;
const square = x => x * x;
const mean = data => data.reduce(sum) / data.length;

Export the function sum by using the ES6 syntax.

// file-1.js
const sum = (x, y) => x + y;
const square = x => x * x;
const mean = data => data.reduce(sum) / data.length;

Export the functions sum and square by using the ES6 syntax.

// file-1.js
const sum = (x, y) => x + y;
const square = x => x * x;
const mean = data => data.reduce(sum) / data.length;

export { sum };

Let us assume that there is a file file-2.js in the same directory as file-1.js. Import the function sum from file-1.js into file-2.js by using the ES6 syntax.

// file-1.js
const sum = (x, y) => x + y;
const square = x => x * x;
const mean = data => data.reduce(sum) / data.length;

export default sum;

Let us assume that there is a file file-2.js in the same directory as file-1.js. Import the function sum from file-1.js into file-2.js by using the ES6 syntax.

// file-1.js
const sum = (x, y) = > x + y;
const square = x = > x * x;
const mean = data => data.reduce(sum) / data.length;

export { sum, square };

Let us assume that there is a file file-2.js in the same directory as file-1.js. Import the functions sum and square from file-1.js into file-2.js by using the ES6 syntax.

const a = 0.4 - 0.3;
const b = 0.3 - 0.2;

console.log (a === b);

What does the previous code display to the screen?

const a = ('a' / 1);
const b = (5 / 0);
const c = (-5 / 0);

console.log(a);
console.log(b);
console.log(c);

console.log(typeof a);
console.log(typeof b);
console.log(typeof c);

What does the previous code display to the screen?

1. We have a variable b. Check if b is equal to NaN.
2. We have a variable c. Check if c is a regular number (different than NaN, Infinity and -Infinity).

Define a function randomIntegerBetween() that has 2 integers as parameters, min and max, and returns a random integer between min and max inclusive.

Create 3 empty objects a, b and c in 3 different ways.

const a = { a1: 1, a2: 2, a3: 3 };
a[Symbol.for("a4")] = 4;

let b = Object.create(a);
b.b1 = 5;
b[Symbol.for("b2")] = 6;

for (let p in b) {
  console.log(p, b[p]);
}

What does the previous code display to the sreen?

const a = {
  a1: 1,
  a2: 2,
  countryCallingCodes: { US: 1, UK: 44 }
};

Create a new object b, which is a deep copy of the object a. In other words, if we ever mutate object a, it does not affect object b.

const a = 1, b = 2, c= 3, d = 4, e = 5;

1. Use the ES6/ES2015 shorthand property names syntax to create an object o that has property names a, b, c, d, e, and property values 1, 2, 3, 4, 5.
2. Create a similar object p, but without using ES6/ES2015 shorthand property names syntax.

const PROPERTY_NAME = 'p1';
const propertyValue = () => 'p' + 2;

Create an object o that has properties names of p1 and p2 and values of 1 and 2. Use PROPERTY_NAME and propertyValue() to do so.

Create an object o that has a property _color with a value of 'green', a simple getter method and a simple setter method.

Display to the screen the color of o, then change it to 'blue' and finally display the new color of o to the screen.

Display to the screen all the properties of the global object of your environment.

const array = [...'abc'];
const object = { k1: 1, k2: 2, k3: 3 };

Without running the code, what does each of the following loop print to the screen?

// Loop 1
for (let value in array) {
  console.log(value);
}

// Loop 2
for (let value of array) {
  console.log(value);
}

// Loop 3
for (let value in object) {
  console.log(value);
}

// Loop 4
for (let value of object) {
  console.log(value);
}

const letters = [...'abcdefghijklmnopqrstuvwxyz'];
const randomIndex = Math.floor(Math.random() * letters.length);
const khaled = Object.assign(
  {},
  {
    [letters[randomIndex]]: 'major key'
  }
);

console.log(khaled);

Write some code to check if the object khaled has the key 'b'. If it does, display to the screen 'Another one'. Otherwise, display to the screen "Don't play yourself".

const twister = 'Betty Botter bought some butter';

Assign the first 3 characters of the string twister to a variable first_3.

const danger = 'Croco-croco-dile';

1. Assign the index of the first letter 'o' of the string danger to a variable a.
2. Assign the index of the last 'co' of the string danger to a variable b.

const tall = 'Giraffe-raffe-gi';

1. Check if the string tall starts with 'Gir' and assign the return value to a variable a.
2. Check if the string string tall ends with '-gi' and assign the return value to a variable b.

const numbers = '12345 34567 56789';

Check if the string numbers includes the characters '345' and assign the return value to a variable t.

const symetry = '--------0|0--------';

Replace the '-' with '_' in the string symetry and assign the return value to a variable t.

const bob = 'I shot the sheriff';

1. Transform the string bob to lower case and assign the return value to a variable lower.
2. Transform the string bob to upper case and assign the return value to a variable upper.

const franck = 'Singing in the rain';

Assign the character at index 5 of the string franck to a variable t.

const snoop = 'Calvin';

Asign the ASCII code of the character at index 4 of the string snoop to a new variable t.

const heisenberg = "I'm in the empire business";

1. Add 3 white spaces at the beginning of heisenberg and assign the new value to a variable a.
2. Add 3 white spaces at the end of heisenberg and assign the new value to a variable b.
3. Add 3 '*' at the beginning of heisenberg and assign the new value to a variable c.
4. Add 3 '!' at the end of heisenberg and assign the new value to a variable d.

const birdy = "   Flying pelican   ";

1. Use a built-in JavaScript method to remove all white spaces at the start and the end of birdy and assign the new value to a variable a.
2. Use a built-in JavaScript method to remove all white spaces only at the start of birdy and assign the new value to a variable b.
3. Use a built-in JavaScript method to remove all white spaces only at the end of birdy and assign the new value to a variable c.

const u = 'Talk ';
const v = 'that talk RiRi! '

1. Concatenate strings u and v and assign the value to a new variable a1.
2. Concatenate strings u and v in a different way and assign the value to a new variable a2.
3. Use a built-in JavaScript method to concatenate string a 3 times and assign the value to a new variable b.

const a = 'one-two-three';

const b = "one-\
two-\
three";

const c = `one-
two-
three`;

const d = "one-\ntwo-\nthree";

console.log(a === b);
console.log(b === c);
console.log(c === d);

What does the previous code print to the screen?

const love = '❤️❤️❤️';
const mula = '$$$';

console.log(love.length);
console.log(mula.length);

What does the previous code print to the screen and why is that?

const a = 'caf\u{e9}';
const b = 'cafe\u{301}';

console.log(a);
console.log(b);

If you run the previous code, you see the string 'café' logged twice on the screen. If we add console.log(a === b); at the end of the previous code, what would be displayed to the screen?

let [a, b] = [1];
const [c, d] = [2, 3, 4];
[a, b] = [b, a];

console.log(a);
console.log(b);
console.log(c);
console.log(d);

What does the previous code display to the screen?

let [e, ...f] = [5, 6, 7, 8];
let [...g] = ['Pluto'];
let [first, ...last] = 'abcd';

console.log(e);
console.log(f);
console.log(g);
console.log(first);
console.log(last);

What does the previous code display to the screen?

const color = {red: 0, green: 10, blue: 20, alpha: 1};
let { yellow, red, blue, alpha } = color;

console.log(yellow);
console.log(red);
console.log(blue);
console.log(alpha);

What does the previous code display to the screen?

let barrow_1 = 'Bonnie';
const barrow_2 = 'Clyde';

barrow_1 = 'Raymond';
console.log(barrow_1);

barrow_2 = 'Ralph';
console.log(barrow_2);

What does the previous code display to the screen?

What variable name is a valid name in JavaScript?

1. 1elephant
2. tallGiraffe_1
3. $crocodile
4. nice-athletic-camel
5. wise_small_hippo
6. zebra2
7. new

const a = ['Giraffe', 10, false, null];
const [b, c, d, e] = a;
const f = a[4];

const g = function() {
  return true;
};

const h = { key_1: 1, key_2: 2 };
const i = Symbol.for('Have you ever used a Symbol?');
const j = 10n;

const values = [a, b, c, d, e, f, g, h, i, j];

for (let value of values) {
  console.log(typeof value);
}

What does the previous code display to the screen?

let dog = 'Spartacus';
let cat;

{
  let dog = 'Crixus';
  cat = 'Oenomaus';
  squirrel = 'Ashur';
}

const reassign = cat => cat = 'Barca';
const changeName = newDog => dog = 'Agron';

reassign(cat);
changeName(dog);

console.log(dog);
console.log(cat);
console.log(squirrel);

What does the previous code print to the screen?

let shouldContinue = true;

setTimeout(() => { shouldContinue = false; }, 200);
  
while(shouldContinue === true) {
  console.log('Looping, looping, looping...')
};

What does the previous code display to the screen?