JavaScript Cheat Sheet

A Programming › JavaScript cheat sheet in English by andrea_25

Dive into the dynamic world of JavaScript with this concise cheat sheet. Packed with fundamental concepts, code snippets, and useful tips, it's designed to be a quick and concise sidekick in your programming journey.

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8,749 views 1,334 downloads 18 Oct 2023 History

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// this is a single line comment

/* this is a multi-line comment */

This code will be ignored. Comments are generally a bad idea, your code should be explicit enough as it is.
More info

Variable creation

let variable = "some value";

let num = 4;

let isTrue = true;

More info

Variable operations

let x = 2;

let y = 3;

let z = x + y;

let city = "Rome";

let country = "Italy";

let place = city + " " + country; // Rome Italy

Variable data types

let age = 92; // Number

let name = "Tommaso"; // String

let canCode = true; // Boolean

More info

Structure types

let students = ["Salvatore", "Leonardo", "Antonella"]; // Array

let kate = { firstName: "Marianna", lastName: "Di Luna", age: 23, canCode: true, }; // Object

More info

Alert

alert("this is an alert)";

let name = "Jack";

alert(name);

More info

Prompt

let firstName = prompt("What's your first name?");

let lastName= prompt("What's your last name?");

let fullName = firstName + " " + lastName;

alert(fullName);

More info

If else statement

let age = prompt("How old are you?");

if (age < 18) {
   alert("You cannot apply"); 
} else {
   alert("You can apply"); 
}

More info

Logical or

if (age < 18 || gender === "male") {
   alert("You can't do that"); 
}

The code will be executed if one statement is true.
More info

Logical and

if (continent === "Europe" && language === "Portuguese") {
   alert("You are from Portugal 🇵🇹"); 
} else {
   alert("You are not from Portugal"); 
}

The code will be executed if both statements are true.
More info

Comparison and logical operators

2 > 3 // false  
2 < 3 // true 
2 <= 2 // true 
3 >= 2 // true 
2 === 5 // false  
2 !== 3 // true 
1 + 2 === 4 // false

More info

Get Date-Time info

let now = new Date();
now.getMinutes(); // 0,1,2, 12
now.getHours(); //1, 2, 3, 4
now.getDate(); //1, 2, 3, 4
now.getDay(); // 0, 1, 2
now.getMonth(); // 0, 1, 2
now.getFullYear(); // 2021

More info

Array

Initialization
let numbers = [5, 10, 15, 20];

Add
numbers.push(25);

Set
numbers[2] = 30;

Delete
delete numbers[1];

Unshift
numbers.unshift(1);

Check Existance
numbers.include(25);

Pop
let lastNumber = numbers.pop(); // Remove the last item

Shift
let removedNumber = numbers.shift(); // Remove the first item

Get Index
let index = numbers.indexOf(15);

Loop

for (let num of numbers) {  
   console.log(num);   
}

Clear
numbers = [];

List

Declaration
let temperatures = new List():

Add

temperatures.add(22);
temperatures.add(25);
temperatures.add(27);
temperatures.add(20);

Set
temperatures.set(2, 26);

Get Item At Index
let temp = temperatures.get(1);

Check Existance
temperatures.contains(27);

Remove
temperatures.remove(20);

Size
temeratures.size();

Loop

for (let temp of temperatures.toArray()) {
     console.log(temp);   
}

Clear
temperatures.clear();

HashSet

Declaration
let travelDestinations = new HashSet();

Add

travelDestinations.add("Paris");
travelDestinations.add("Tokyo");
travelDestinations.add("New York");
travelDestinations.add("Sydney");

Values
travelDestinations.values();

Delete
travelDestinations.delete("Sydney");

Size
travelDestination.size();

Loop

for (let city of travelDestinations.values()) {
     console.log(`Travel to: ${city}`);   
}

Clear
travelDestination.clear();

Queue

Declaration
let bankQueue = new Queue();

Enqueue

bankQueue.enqueue("John");
bankQueue.enqueue("Emma");
bankQueue.enqueue("Lucas");
bankQueue.enqueue("Sophia");

Dequeue
bankQueue.dequeue();

Front
bankQueue.front(); // Get the front of the queue

Check Existance
bankQueue.contains("Emma");

Size
bankQueue.size();

LinkedList

Declaration
let train = new LinkedList();

Append

train.append("Engine Car");
train.append("Passenger Car 1");
train.append("Dining Car");
train.append("Passenger Car 2");
train.append("Cargo Car");

Head
let car = train.getHead();

Get At Index
let car = train.getAt(2);

Add At Index
train.addAt(3, "Luxury Car");

Prepend
train.prepend("Pilot Car"); // Add at the front

Remove
train.remove("Dining Car");

Remove At Index
train.removeAt(2);

Contains
train.contains("Dining Car");

Loop

for (let car of train) {
     console.log(`Inspecting car: ${car}`);   
}

Dictionary

Declaration
let bookAuthors = new Dictionary();

Add

bookAuthors.add("Harry Potter", "J.K. Rowling");
bookAuthors.add("The Hobbit", "J.R.R. Tolkien");
bookAuthors.add("Dune", "Frank Herbert");

Check Existance Key
bookAuthors.hasKey("Dune");

Check Existance Value
bookAuthors.hasValue("J.K. Rowling");

Remove Pair
bookAuthors.remove("The Hobbit");

Keys
bookAuthors.keys();

Values
bookAuthors.values();

Entries
bookAuthors.entries();

Size
bookAuthors.size();

Clear
bookAuthors.clear();

SortedList

Initialization with custom comparator

const byPageCount = (a, b) => a.pages - b.pages;
let bookshelf = new SortedList(byPageCount);

Add

let book1 = { title: "Short Stories", pages: 150 };
let book2 = { title: "Novel", pages: 320 };
let book3 = { title: "Poems", pages: 80 };
let book4 = { title: "Long Novel", pages: 480 };
bookshelf.add(book1);
bookshelf.add(book2);
bookshelf.add(book3);

Get At Index
let selectedBook = bookshelf.get(0);

Contains
bookshelf.contains(book3);

Remove
bookshelf.remove(book3);

Min
let smallestBook = bookshelf.min();

Max
let largestBook = bookshelf.max();

Size
bookshelf.size();

Loop

for (let book of bookshelf.toArray()) {
     console.log(`${book.title} (${book.pages} pages)`);   
}

Clear
bookshelf.clear();

SortedSet

Initialization with a custom comparator

const byScore = (a, b) => a - b;
let examScores = new SortedSet(byScore);

Add

examScores.add(92);
examScores.add(85);
examScores.add(78);
examScores.add(92);

Check Existance
examScores.has(85);

Delete
examScores.delete(78);

Min
examScores.min();

Max
examScores.max();

Size
examScores.size();

Loop

for (let score of examScores.toArray()) {
     console.log(`Exam score: ${score}`);   
}

Clear
examScores.clear();

Stack

Declaration
let browsingHistory = new Stack();

Push

browsingHistory.push("https://www.example.com");
browsingHistory.push("https://www.google.com");
browsingHistory.push("https://www.stackoverflow.com");

Peek
let first = browsingHistory.peek();

Pop
let item = browsingHistory.pop();

Size
browsingHistory.size();

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