Learning Java Script:Length,Variable,Array ,Math and Random

In JavaScript, .length is a commonly used property that returns the number of elements in an array, the number of characters in a string, or the number of arguments in a function, depending on the context.

1. String Length

Returns the number of characters in a string:

let str = "Hello, world!";
console.log(str.length); // Output: 13

2. Array Length

Returns the number of elements in an array:

let arr = [1, 2, 3, 4];
console.log(arr.length); // Output: 4

You can also change the length of an array:

arr.length = 2;
console.log(arr); // Output: [1, 2]

3. Function Length

Returns the number of expected arguments in a function:

function myFunc(a, b, c) {}
console.log(myFunc.length); // Output: 3

In JavaScript, variables are used to store data values. You can declare a variable using one of three keywords:

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1. var (Old, avoid if possible)

var name = "Alice";

• Function-scoped
• Can be redeclared and updated
• Gets hoisted (but initialized with undefined)

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2. let (Preferred for variables that change)

let age = 25;
age = 26; // OK

• Block-scoped
• Can be updated, but not redeclared in the same scope

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3. const (Preferred for constants)

const pi = 3.14159;
// pi = 3; //  Error

• Block-scoped
• Cannot be updated or redeclared
• For arrays/objects: you can change contents, but not reassign

const person = { name: "Alice" };
person.name = "Bob"; //  Allowed
// person = { name: "Charlie" }; // Error

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Best Practice

• Use **const** by default
• Use **let** only when you know the variable will change
• Avoid **var** unless you’re dealing with old codebases

An array in JavaScript is a special variable used to store multiple values in a single variable. Arrays are zero-indexed and can hold elements of any data type, including numbers, strings, objects, or even other arrays.

Creating an Array

// Using array literal
let fruits = ["apple", "banana", "cherry"];

// Using the Array constructor
let numbers = new Array(1, 2, 3, 4);

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Accessing Elements

console.log(fruits[0]); // "apple"
console.log(fruits[2]); // "cherry"

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Modifying Elements

fruits[1] = "blueberry";
console.log(fruits); // ["apple", "blueberry", "cherry"]

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Example

let colors = ["red", "green", "blue"];
colors.push("yellow");
console.log(colors); // ["red", "green", "blue", "yellow"]

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In JavaScript, the Math object and Math.random() function are used for performing mathematical operations and generating random numbers.

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Math Object in JavaScript

The Math object provides properties and methods for mathematical constants and functions. It is not a constructor, so you don't use new Math().

Math.random() in JavaScript

Math.random() returns a floating-point number between 0 (inclusive) and 1 (exclusive).

Examples

// Random number between 0 and 1
let rand = Math.random();

// Random number between 0 and 100
let rand100 = Math.random() * 100;

// Random integer between 1 and 10
let randInt = Math.floor(Math.random() * 10) + 1;

console.log(rand, rand100, randInt);

Random Integer Function

You can create a reusable function to get a random integer in a range:

function getRandomInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

console.log(getRandomInt(5, 15)); // Random integer between 5 and 15

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