JavaScript examples / cookbook

let example = {
    intField: 1,
    strField: "hello",
    boolField: false
};

console.log("default javascript representation");
console.log(example);

// to json
let exampleJson = JSON.stringify(example, null, 2);
console.log("json:");
console.log(exampleJson);

// load json
let parsedObj = JSON.parse(exampleJson);
if (parsedObj['intField'] !== example['intField']) {
    throw new Error("Assertion failed");
}

exampleJson;

const fruits = ["apple", "banana", "cherry", "date", "elderberry"];

// 1. Using a for loop
console.log("Using a for loop:");
for (let i = 0; i < fruits.length; i++) {
    console.log(fruits[i]);
}

console.log("Using a for...of loop:");
// 2. Using a for...of loop
for (const fruit of fruits) {
    console.log(fruit);
}

console.log("Using forEach method:");
// 3. Using forEach method
fruits.forEach(function(fruit) {
    console.log(fruit);
});

console.log("Using map method (typically for transforming array):");
// 4. Using map method (typically for transforming array, but we'll use it for iteration here)
fruits.map(fruit => {
    console.log(fruit);
    return fruit; // Map requires a return, though in this case we're not saving the result
});

console.log("Using for...in loop (not recommended for arrays, but possible):");
// 5. Using for...in loop (not recommended for arrays due to possibility of iterating over non-index properties)
for (const index in fruits) {
    console.log(fruits[index]);
}
fruits;

// Example JavaScript code to demonstrate how to use regex to validate email addresses

// Function to validate email address using regex
function validateEmail(email) {
  // Define the regular expression for validating an email
  // The regex pattern explained:
  // ^ asserts position at start of the string
  // [a-zA-Z0-9._%+-]+ matches one or more of the allowed characters before the @
  // @ matches the literal @ symbol
  // [a-zA-Z0-9.-]+ matches one or more of the allowed characters for the domain part
  // . matches the literal dot symbol
  // [a-zA-Z]{2,} matches two or more alphabetic characters for the top-level domain
  // $ asserts position at the end of the string
  const emailRegex = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,}$/;

  // Test the email against the regex pattern
  const isValid = emailRegex.test(email);

  // Log the regex pattern used for validation
  console.log("Regex Pattern: ", emailRegex);

  // Log the email being tested and whether it is valid
  console.log("Testing Email: ", email);
  console.log("Is Valid: ", isValid);

  return isValid;
}

// Example email inputs to test the validation function
const testEmails = [
  "test@example.com",       // Valid email
  "user.name@domain.co",    // Valid email
  "invalid-email@",         // Invalid email (missing domain part)
  "@example.com",           // Invalid email (missing local part)
  "user@domain@domain.com", // Invalid email (multiple @ symbols)
  "user@domain.c",          // Invalid email (top-level domain too short)
];

// Loop through each test email and validate it
testEmails.forEach(email => {
  console.log("\n---\n");
  validateEmail(email);
});

// Example JavaScript code to demonstrate different ways to iterate over an object's key-value pairs

// Define an object with some key-value pairs
const person = {
  name: "Alice",
  age: 30,
  occupation: "Engineer"
};

// Using for...in loop to iterate over the object's keys
console.log("Using for...in loop:");
for (const key in person) {
  if (person.hasOwnProperty(key)) { // Check if the property is directly on the object
    console.log(`Key: ${key}, Value: ${person[key]}`);
  }
}

// Using Object.keys() method to get an array of keys and forEach to iterate
console.log("\nUsing Object.keys() and forEach:");
Object.keys(person).forEach(key => {
  console.log(`Key: ${key}, Value: ${person[key]}`);
});

// Using Object.values() method to get an array of values and forEach to iterate
console.log("\nUsing Object.values() and forEach:");
Object.values(person).forEach(value => {
  console.log(`Value: ${value}`);
});

// Using Object.entries() method to get an array of [key, value] pairs and forEach to iterate
console.log("\nUsing Object.entries() and forEach:");
Object.entries(person).forEach(([key, value]) => {
  console.log(`Key: ${key}, Value: ${value}`);
});

// Using for...of loop with Object.entries() to iterate over [key, value] pairs
console.log("\nUsing for...of loop with Object.entries():");
for (const [key, value] of Object.entries(person)) {
  console.log(`Key: ${key}, Value: ${value}`);
}

// Using for...of loop with Object.keys() to iterate over keys and access values
console.log("\nUsing for...of loop with Object.keys():");
for (const key of Object.keys(person)) {
  console.log(`Key: ${key}, Value: ${person[key]}`);
}

// Using for...of loop with Object.values() to iterate over values
console.log("\nUsing for...of loop with Object.values():");
for (const value of Object.values(person)) {
  console.log(`Value: ${value}`);
}