JavaScript

JavaScript is a versatile, high-level, interpreted programming language primarily used for client-side web development. It enables interactive and dynamic features on websites, making them more engaging for users. Developed in the mid-'90s, JavaScript has evolved into a key technology for building modern web applications.

Variables and Operations

• What is a variable, and what is it for?

Variables are memory spaces where we can store information, depending on the types and data structures supported by our language.

• Difference between declaring and initializing a variable?

Declaring is telling JavaScript we're creating a variable with a specific name. Initializing is giving that variable a value.

• Difference between adding numbers and concatenating strings?

The + operator allows us to add numbers and concatenate strings. When used with numbers, it adds them. With strings, it joins (concatenates) them.

Declaration and Assignment

Reserved word for a variable, depending on the case, can be:

• var
• let
• const

var my_variable = "Declare variable";

Variable name: var my_variable

Assignment operator: =

Data assigned to the variable: "Declare variable"

Naming and data types:

Number:

JavaScript handles both integers and decimals as numbers.

let age = 40;
let temperature = 25.5;

String:

Strings can hold anything from a single character to a whole paragraph.

let name = "Luis";
let greeting = "Hello, world!";

Boolean:

Booleans are great for conditions, like checking if it's sunny or raining.

let isSunny = true;
let isRaining = false;

Null and Undefined:

let nothing = null; // You might use this when you intentionally want to say, "There's nothing here."
let notDefined; // If you declare a variable but don't assign a value, it's undefined.

Array:

Arrays can store multiple values, making it easy to work with lists of items.

let favoriteFruits = ["Apple", "Banana", "Orange"];

Object:

Objects help you organize data with named properties. Here, we have a person with a name, age, and student status.

let myObject = {
    name: "Luis",
    age: 20,
    isStudent: true
  };

Functions:

Functions are a type of data in JavaScript. They can be assigned to variables and passed around in your code.

let greet = function() {
  console.log("Hello!");
};

Date:

The Date type is used for working with dates and times.

let currentDate = new Date();

RegExp (Regular Expression):

Regular expressions are used for pattern matching within strings.

let pattern = /[a-zA-Z]+/;

Example: JavaScript code for variables:

let name = 'Juan Sultan';
let lastName = 'Galeas Zabala';
let username = 'juandc';
let age = 19;
let email = 'crespo@gmail.xyz';
let isLegalAge = true;
let savedMoney = 1000;
let debts = 100;

Example: Calculations:

let fullName = name + ' ' + lastName;
let realMoney = savedMoney - debts;

Functions

• What is a function?

A function is like a recipe – a set of instructions to perform a specific task.

• When is it useful to use a function in my code?

Use functions to avoid repeating code, make it more readable, and organize tasks logically.

• Difference between parameters and arguments of a function?

Parameters are placeholders in a function definition, and arguments are the actual values passed when calling the function.

Converting code into a function:

function introduceYourself(name, lastName, nickname) {
  let completeName = name + ' ' + lastName;
  console.log("My name is " + completeName + ", but I prefer you to call me " + nickname + ".");
}

Conditionals

• What is a conditional?

A conditional is a decision-making structure in code.

• Types of conditionals in JavaScript and differences?

In JavaScript, there are if, else if, and else. They handle different conditions sequentially.

• Can I combine functions and conditionals?

Absolutely, you can use functions to encapsulate tasks within conditionals.

const subscriptionType = "Basic";

if (subscriptionType === "Free") {
  console.log("You can only take free courses.");
} else if (subscriptionType === "Basic") {
  console.log("You can take almost all Platzi courses for a month.");
} else if (subscriptionType === "Expert") {
  console.log("You can take almost all Platzi courses for a year.");
} else if (subscriptionType === "ExpertPlus") {
  console.log("You and someone else can take ALL Platzi courses for a year.");
}

Enhance else and else if:

/*
"lookup table" or "dictionary."
It's essentially a mapping between keys (subscription types) and values (associated messages).

This approach leverages the key-based retrieval capabilities of objects, providing a cleaner and more efficient way to manage multiple conditions.
*/

// Subscription information object
const subscriptionInfo = {
  Free: "You can only take free courses.",
  Basic: "You can take almost all Platzi courses for a month.",
  Expert: "You can take almost all Platzi courses for a year.",
  ExpertPlus: "You and someone else can take ALL Platzi courses for a year."
};

// Function to check and display subscription information
function checkSubscription(subscriptionType) {
  const message = subscriptionInfo[subscriptionType];
  if (message) {
    console.log(message);
  } else {
    console.log("Invalid subscription type.");
  }
}

// Example usage:
checkSubscription("Free");
checkSubscription("Basic");
checkSubscription("Expert");
checkSubscription("ExpertPlus");
checkSubscription("InvalidType");

Loops

• What is a loop?

A loop is a way to repeatedly execute a block of code.

• Types of loops in JavaScript?

Common loops are for, while, and do-while.

• What is an infinite loop, and why is it a problem?

An infinite loop never stops, causing the program to run indefinitely, often leading to system or application crashes.

• Can I mix loops and conditionals?

Absolutely, combining loops and conditionals is common for complex logic.

Converting for loops to while:

// for loop
for (let i = 0; i < 5; i++) {
    console.log("El valor de i es: " + i);
}

for (let i = 10; i >= 2; i--) {
    console.log("El valor de i es: " + i);
}

// while loop
let i = 0;
while (i < 5) {
  console.log("The value of i is: " + i);
  i++;
}

let j = 10;
while (j >= 2) {
  console.log("The value of j is: " + j);
  j--;
}

Example: Asking users about 2 + 2 until correct:

let userAnswer;
do {
  userAnswer = prompt("What is 2 + 2?");
} while (userAnswer !== "4");

alert("Congratulations! You got it right!");

Lists

• What is an array?

An array is a data structure that stores a collection of elements.

• What is an object?

An object is a collection of key-value pairs, often representing real-world entities.

• When is it better to use objects or arrays?

Use arrays for ordered lists of similar items; use objects for key-value pairs representing attributes of a single entity.

• Can I mix arrays with objects or even objects with arrays?

Absolutely, you can have arrays of objects or objects containing arrays.

Example: Function to print the first element of any array:

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

function printFirstElement(arr) {
  console.log(arr[0]);
}

printFirstElement(myArray);

Example: Function to print all elements of any array:

let anotherArray = ['apple', 'orange', 'banana'];

function printAllElements(arr) {
  for (let element of arr) {
    console.log(element);
  }
}

printAllElements(anotherArray);

Example: Function to print all elements of any object:

function printAllObjectElements(obj) {
  for (let key in obj) {
    console.log(obj[key]);
  }
}

// Example usage:
let myObject = { key1: 'value1', key2: 'value2', key3: 'value3' };
printAllObjectElements(myObject);

Best Practices

• The variable name should be descriptive and related to the code.
• Variables cannot start with numbers.
• Special characters cannot be used.
• Writing styles for a variable are: lowerCamelCase, UpperCamelCase, snake_case.