Arrays.md

Arrays in Detail

JavaScript array is an object that represents a collection of similar type of elements.

let months = ["January", "February", "March", "April"];

for (let i = 0; i < months.length; i++) {
  console.log(months[i]);
}
// January
// February
// March
// April

Array-Methods

const names = ["John", "Bob", "David", "Mark"];

// Array Push - Adds a new element containing
// the entered value to the end of the array
names.push("Shubham");
console.log(names); // [ 'John', 'Bob', 'David', 'Mark', 'Shubham' ]

// Array Pop - Deletes the last element of an array
names.pop();
console.log(names); // [ 'John', 'Bob', 'David', 'Mark' ]

// Array Shift - deletes the first element of the array
names.shift();
console.log(names); // [ 'Bob', 'David', 'Mark' ]

// Array Unshift - adds the new value to the start of the array
names.unshift("Samarth");
console.log(names); // [ 'Samarth', 'Bob', 'David', 'Mark' ]

// Array Splice - It adds or removes values in any position of an array
names.splice(2, 0, "Shruti", "Rishi");
console.log(names); // [ 'Samarth', 'Bob', 'Shruti', 'Rishi', 'David', 'Mark' ]

names.splice(2, 2);
console.log(names); // [ 'Samarth', 'Bob', 'David', 'Mark' ]

// Array Slice - Copies certain part of an array into a newly created array
const noOneLikesSam = names.slice(1);
console.log(noOneLikesSam); // [ 'Bob', 'David', 'Mark' ]

forEach method

const numbers = [2, 4, 6, 8];

numbers.forEach((value, i) => console.log(value, i)); // prints all the values and indexes

// when to use forEach :
// You want to do something with each element in the array

// Don't use when :
// You want to stop or break the loop when some condition is true.
// When you are working with async code.

let sum = 0;
numbers.forEach((value) => (sum += value));
console.log(sum); // 20

Map method

const inventory = [
  { price: 7, name: "egg" },
  { price: 10, name: "lays" },
  { price: 12, name: "maggie" },
];

// Array Map
const prices = inventory.map((item) => console.log(item.price)); // displays only the prices
const names = inventory.map((item) => console.log(item.name)); // diplays only the names

Array Filter

const numbers = [2, 5, -2, 0, -5, 1];

const positiveNumbers = numbers.filter((number) => number >= 0);
console.log(positiveNumbers);

const negativeNumbers = numbers.filter((number) => number <= 0);
console.log(negativeNumbers);

// Another real life example
const employeesData = [
  { name: "Shubham", overtime: 5 },
  { name: "Samarth", overtime: 7 },
  { name: "Seema", overtime: 8 },
];

const employeesToReward = employeesData.filter(
  (employee) => employee.overtime >= 7
);

const employeeNames = employeesToReward.map((employee) => employee.name);

employeeNames.forEach((user) => {
  console.log(`Congratulations, ${user}`); // Congratulations, Samarth
  // Congratulations, Seema
});

Array Find

// Array Find

// The Find method for arrays returns the
// first value that satisfies the condition

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

const value = numbers.find((number) => number > 5);
console.log(value); // 6

const cities = ["Bangalore", "Mumbai", "New Delhi", "Noida", "Hyderabad"];

const city = cities.find((city) => city.startsWith("N"));

console.log(city); // New Delhi

Array Includes

// Array Includes
const movies = ["Avengers", "Superman", "Batman"];

if (movies.includes("Avengers")) {
  console.log("The movie is available on prime"); // The movie is available on prime
} else {
  console.log("The movie is not available on prime.");
}

// Note Includes method is case sensitive

Array Sort

// Array sort => Alphabetically,
// doesn't sort numbers
// This sort method mutates the original array
const names = ["Shubham", "Aditya", "Shruti", "Samarth"];
names.sort();
console.log(names); // [ 'Aditya', 'Shruti', 'Samarth', 'Shubham' ]

const numbers = [4, 12, 8, 5, 1];

// Ascending order
numbers.sort((a, b) => a - b);
console.log(numbers); // [ 1, 4, 5, 8, 12 ]

// Descending order
numbers.sort((a, b) => b - a);
console.log(numbers); // [ 12, 8, 5, 4, 1 ]

Some and Every

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

// Array Some => returns true if atleast one element passes the test
console.log(array.some((number) => number > 5)); // false

// Array Every => return true if all elements pass the test
console.log(array.every((number) => number > 0)); // true

Array Reduce

// Array Reduce

const groceryList = [29, 12, 45, 35, 87, 110];

const total = groceryList.reduce((total, price) => total + price, 0);

console.log(total); // 318

All the code blocks above demonstrates how to use arrays and various array methods in JavaScript. An array is an object that represents a collection of similar type of elements. The code first defines an array months and then uses a for loop to iterate over the array, printing each element to the console. The code then demonstrates several array methods including push, pop, shift, unshift, splice, slice, forEach, map, filter, and find. The push method adds a new element to the end of the array, the pop method removes the last element of an array, the shift method removes the first element of an array, the unshift method adds a new value to the start of the array, the splice method adds or removes elements in any position of the array, the slice method copies a certain part of an array into a new array, the forEach method executes a provided function once for each array element, the map method creates a new array with the results of calling a provided function on every element in the array, the filter method creates a new array with all elements that pass the test implemented by the provided function, and the find method returns the first element in the array that satisfies a provided testing function.