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JavaScript and MySQL

Arrays

In JavaScript, an array is a special variable that can hold more than one value at a time. Arrays are used to store multiple values in a single variable. These values can be of various types, including other arrays, and they're maintained in an ordered collection. Here's how you work with arrays in JavaScript:

Creating an Array

You can create an array by using the array literal syntax, or the Array constructor.

Array Literal Syntax (preferred way because it's more concise):

let fruits = ["Apple", "Banana", "Mango"];

Array Constructor:

let vegetables = new Array("Carrot", "Pea");

Accessing Array Elements

You can access an element in an array by referring to the index number. This reference is zero-based, meaning that the first element has the index 0, the second has index 1, and so on.

let fruits = ["Apple", "Banana", "Mango"];
let firstFruit = fruits[0]; // "Apple"

Changing an Array Element

Similarly, you can change the value of a specific element in an array by using the index number.

fruits[1] = "Strawberry"; // Now the array is ["Apple", "Strawberry", "Mango"]

Accessing the Full Array

If you want to access the whole array, you can just use the array's name:

console.log(fruits); // ["Apple", "Strawberry", "Mango"]

Array Properties and Methods

Arrays have properties and methods that you can use to manipulate them. Here are a few common ones:

length: This property returns the number of elements in the array.

let count = fruits.length; // 3

push(): This method adds a new element to the end of an array.

fruits.push("Orange"); // ["Apple", "Strawberry", "Mango", "Orange"]

pop(): This method removes the last element from an array.

fruits.pop(); // Removes "Orange" from the fruits array

shift(): This method removes the first item of an array.

fruits.shift(); // Removes "Apple" from the fruits array

unshift(): This method adds a new item at the beginning of an array.

fruits.unshift("Pineapple"); // Adds "Pineapple" at the beginning of the fruits array

indexOf(): This method searches the array for an element and returns its first index. If it's not found, it returns -1.

let pos = fruits.indexOf("Mango"); // 1

splice(): This method can be used to add new items to an array or remove existing items.

fruits.splice(1, 1, "Peach"); // Removes "Strawberry" at index 1 and adds "Peach" at that position

Iterating Over an Array

To loop through each item in an array, you can use a simple for loop, for...of loop, or the forEach() method, among others.

// for loop
for (let i = 0; i < fruits.length; i++) {
 console.log(fruits[i]);
}
// for...of loop
for (let fruit of fruits) {
 console.log(fruit);
}
// forEach() method
fruits.forEach(function(item, index, array) {
 console.log(item, index);
});

Arrays in JavaScript are versatile and powerful, and they include many more methods than what's listed here. They are a fundamental part of the language and are used to store and manipulate collections of data efficiently.