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:
✅ 1. var
(Old, avoid if possible)
var name = "Alice";
- Function-scoped
- Can be redeclared and updated
- Gets hoisted (but initialized with
undefined
)
✅ 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
✅ 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
🧠 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);
🔹 Accessing Elements
console.log(fruits[0]); // "apple"
console.log(fruits[2]); // "cherry"
🔹 Modifying Elements
fruits[1] = "blueberry";
console.log(fruits); // ["apple", "blueberry", "cherry"]
🔹 Example
let colors = ["red", "green", "blue"];
colors.push("yellow");
console.log(colors); // ["red", "green", "blue", "yellow"]
In JavaScript, the Math
object and Math.random()
function are used for performing mathematical operations and generating random numbers.
📐 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
Top comments (0)