What are Array in JavaScript and their Types

let fruits = ["apple", "banana", "orange"];
let numbers = [1, 2, 3, 4, 5];
let mixed = [1, "hello", true, {name: "John"}, null];

let arr = [1, 2, 3, 4, 5];
let empty = [];
let mixed = [1, "hello", true, {x: 10}];

let arr = new Array(1, 2, 3, 4, 5);
let arr2 = new Array(5); // Creates array with 5 empty slots

let arr = Array.of(1, 2, 3);
console.log(arr); // [1, 2, 3]

let str = "hello";
let arr = Array.from(str);
console.log(arr); // ["h", "e", "l", "l", "o"]

let arr2 = Array.from([1, 2, 3], x => x * 2);
console.log(arr2); // [2, 4, 6]

let colors = ["red", "green", "blue"];
console.log(colors[0]); // red
console.log(colors.length); // 3

let matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
];
console.log(matrix[0][0]);  // 1 
console.log(matrix[1][2]);  // 6 

let cube = [
  [[1, 2], [3, 4]],
  [[5, 6], [7, 8]]
];
console.log(cube[0][0][1]);  // 2 
console.log(cube[1][1][0]);  // 7 

let jagged = [
  [1, 2],
  [3, 4, 5],
  [6],
  [7, 8, 9, 10]
];
console.log(jagged[0].length);  // 2 
console.log(jagged[1].length);  // 3 

let person = [];
person["name"] = "John";
person["age"] = 30;
person["city"] = "New York";
console.log(person.name);  // John 
 // Note: Better to use objects for key-value pairs 

let sparse = [1, , , 4, 5];
console.log(sparse.length);  // 5 
console.log(sparse[1]);  // undefined 

let arr = [1, 2, 3, 4, 5];
console.log(arr.length);  // 5 
arr.length = 3;  // Truncates array 
console.log(arr);  // [1, 2, 3] 

let arr = [1, 2, 3];
arr.push(4, 5);
console.log(arr); // [1, 2, 3, 4, 5]

let arr = [1, 2, 3];
let last = arr.pop();
console.log(last);  // 3 
console.log(arr);  // [1, 2] 

let arr = [2, 3];
arr.unshift(0, 1);
console.log(arr); // [0, 1, 2, 3]

let arr = [1, 2, 3];
let first = arr.shift();
console.log(first);  // 1 
console.log(arr);  // [2, 3] 

let arr = [1, 2, 3, 4, 5];
arr.splice(2, 1, "a", "b");  // Remove 1 element at index 2, add "a", "b" 
console.log(arr);  // [1, 2, "a", "b", 4, 5] 

let arr = [1, 2, 3, 4, 5];
console.log(arr.at(0));  // 1 
console.log(arr.at(-1));  // 5 
console.log(arr.at(-2));  // 4 

let arr = [1, 2, 3, 2, 1];
console.log(arr.indexOf(2));  // 1 
console.log(arr.indexOf(5));  // -1 

let arr = [1, 2, 3, 2, 1];
console.log(arr.lastIndexOf(2)); // 3

let arr = [1, 2, 3, 4, 5];
console.log(arr.includes(3));  // true 
console.log(arr.includes(10));  // false 

let arr = [1, 5, 10, 15];
let result = arr.find(x => x > 8);
console.log(result);  // 10 

let arr = [1, 5, 10, 15];
let index = arr.findIndex(x => x > 8);
console.log(index); // 2

let numbers = [1, 2, 3, 4];
let doubled = numbers.map(x => x * 2);
console.log(doubled); // [2, 4, 6, 8]

let numbers = [1, 2, 3, 4, 5];
let evens = numbers.filter(x => x % 2 === 0);
console.log(evens); // [2, 4]

let numbers = [1, 2, 3, 4];
let sum = numbers.reduce((acc, curr) => acc + curr, 0);
console.log(sum); // 1

let arr = [1, 2, 3];
let result = arr.reduceRight((acc, curr) => acc + curr, 0);
console.log(result); // 6

let arr = [1, 2, 3];
let result = arr.flatMap(x => [x, x * 2]);
console.log(result); // [1, 2, 2, 4, 3, 6]

let arr1 = [1, 2];
let arr2 = [3, 4];
let combined = arr1.concat(arr2, [5, 6]);
console.log(combined); // [1, 2, 3, 4, 5, 6]

let arr = ["a", "b", "c"];
console.log(arr.join());  // a,b,c 
console.log(arr.join("-"));  // a-b-c 
console.log(arr.join(""));  // abc 

let nested = [1, [2, 3], [4, [5, 6]]];
console.log(nested.flat());  // [1, 2, 3, 4, [5, 6]] 
console.log(nested.flat(2));  // [1, 2, 3, 4, 5, 6] 

let arr = [1, 2, 3];
arr.forEach((element, index) => {
  console.log(index, element);
});
// 0 1, 1 2, 2 3

let arr = [1, 2, 3];
for (let value of arr) {
  console.log(value);
}

let arr = [1, 2, 3];
for (let index in arr) {
  console.log(index, arr[index]);
}

let numbers = [2, 4, 6, 8];
console.log(numbers.every(x => x % 2 === 0)); // true

let numbers = [1, 3, 4, 5];
console.log(numbers.some(x => x % 2 === 0)); // true (4 is even)

let numbers = [3, 1, 4, 1, 5];
numbers.sort((a, b) => a - b);
console.log(numbers);  // [1, 1, 3, 4, 5] 

let strings = ["banana", "apple", "cherry"];
strings.sort();
console.log(strings);  // ["apple", "banana", "cherry"] 

let arr = [1, 2, 3];
arr.reverse();
console.log(arr); // [3, 2, 1]

let arr = [1, 2, 3, 4, 5];
let copy = arr.slice(1, 4);
console.log(copy);  // [2, 3, 4] 

let fullCopy = arr.slice();
console.log(fullCopy);  // [1, 2, 3, 4, 5] 

let arr = [1, 2, 3];
let copy = [...arr];
console.log(copy);  // [1, 2, 3] 

let combined = [...arr, 4, 5];
console.log(combined);  // [1, 2, 3, 4, 5] 

let arr = new Array(5);
arr.fill(0);
console.log(arr); // [0, 0, 0, 0, 0]

let arr = ["a", "b", "c"];
console.log([...arr.keys()]); // [0, 1, 2]
console.log([...arr.values()]); // ["a", "b", "c"]
console.log([...arr.entries()]); // [[0,"a"], [1,"b"], [2,"c"]]

let arr = [1, 2, 3];
console.log(arr.toString()); // "1,2,3"

let arr = [1, 2, 3, 4, 5];
arr.copyWithin(0, 3, 5);
console.log(arr); // [4, 5, 3, 4, 5]

let users = [
  {id: 1, name: "John", age: 30},
  {id: 2, name: "Jane", age: 25},
  {id: 3, name: "Bob", age: 35}
];

 // Get names 
let names = users.map(user => user.name);
console.log(names);  // ["John", "Jane", "Bob"] 

 // Filter users above 25 
let over25 = users.filter(user => user.age > 25);
console.log(over25);  // John and Bob's objects 

let numbers = [1, 2, 3, 4, 5, 6];
let result = numbers
  .filter(x => x > 2)
  .map(x => x * 2)
  .reduce((sum, x) => sum + x, 0);
console.log(result);  // (3*2 + 4*2 + 5*2 + 6*2) = 36 

let matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
];

 // Access element 
console.log(matrix[1][2]);  // 6 

 // Modify element 
matrix[2][0] = 70;
console.log(matrix[2]);  // [70, 8, 9]