? JavaScript Math Object and Math.random()

⚡ Quick Overview

The Math object in JavaScript provides built-in properties (constants) and methods (functions) for common mathematical operations such as rounding, powers, square roots, absolute values, and random number generation using Math.random(). It is a static utility object, so you use it directly as Math.something, not by creating instances.

? Key Concepts

Math is a built-in static object; you never use new Math().
Math properties (like Math.PI, Math.E, Math.SQRT2) are constants, not functions.
Math methods (like Math.round(), Math.floor(), Math.sqrt(), Math.abs()) perform numeric operations.
Math.random() returns a pseudo-random number in the range [0, 1) (0 inclusive, 1 exclusive).
You can combine Math.random() with Math.floor() to produce random integers in any range you want.

? Syntax and Theory

The general pattern for using the Math object is:

result = Math.methodName(value);

Properties (constants): accessed without parentheses, e.g., Math.PI, Math.E, Math.SQRT2.
Methods (functions): always called with parentheses, e.g., Math.round(4.6), Math.sqrt(16).
No instantiation: Math is not a constructor. This is invalid: new Math().

A common pattern for generating a random integer between two values is:

Math.floor(Math.random() * (max - min + 1)) + min

? Code Examples

? Math Properties and Basic Methods

? View Code Example

// Math properties (constants)
console.log(Math.PI);      // 3.141592653589793
console.log(Math.E);       // 2.718281828459045
console.log(Math.SQRT2);   // 1.4142135623730951
console.log(Math.LN2);     // 0.6931471805599453

// Math methods
console.log(Math.round(4.6));   // 5  (nearest integer)
console.log(Math.ceil(4.1));    // 5  (round up)
console.log(Math.floor(4.9));   // 4  (round down)
console.log(Math.trunc(4.9));   // 4  (remove decimals)
console.log(Math.pow(2, 3));    // 8  (2 to the power of 3)
console.log(Math.sqrt(16));     // 4  (square root)
console.log(Math.abs(-7));      // 7  (absolute value)

console.log(Math.max(1, 5, 9)); // 9  (largest value)
console.log(Math.min(1, 5, 9)); // 1  (smallest value)

? Math.random() Basics

? View Code Example

// A random number between 0 (inclusive) and 1 (exclusive)
console.log(Math.random()); // e.g., 0.47283478

// Random integer between 0 and 9
const random0to9 = Math.floor(Math.random() * 10);
console.log(random0to9);

// Random integer between 1 and 100
const random1to100 = Math.floor(Math.random() * 100) + 1;
console.log(random1to100);

// Helper: random integer between min and max (inclusive)
function getRandomInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

console.log(getRandomInt(1, 6));    // e.g., 4 (like a dice roll)
console.log(getRandomInt(50, 100)); // e.g., 73

? More Random Examples

? View Code Example

// Random item from an array
const colors = ["Red", "Green", "Blue"];
const randomIndex = Math.floor(Math.random() * colors.length);
const randomColor = colors[randomIndex];
console.log(randomColor);

// Dice roll (1 to 6)
const dice = Math.floor(Math.random() * 6) + 1;
console.log("Rolled:", dice);

? Live Output and Explanation

? What the code does

Math.PI, Math.E, Math.SQRT2, and Math.LN2 give you commonly used mathematical constants.
Math.round(), Math.floor(), Math.ceil(), and Math.trunc() help you control how decimal numbers are converted to integers.
Math.max() and Math.min() find the largest and smallest values from a list of numbers.
Math.random() on its own returns a decimal between 0 and 1. Multiplying it and using Math.floor() lets you create integer ranges.
The helper getRandomInt(min, max) function wraps this pattern into a reusable piece of code for any integer range.
In the array example, a random index based on colors.length is used to pick a random color from the list.

? Interactive Example

? Roll a Virtual Dice

Click the button to roll a dice (values from 1 to 6) using Math.random() and Math.floor().

Current roll: -

? Tips & Best Practices

Math is not a constructor; never use new Math().
Use Math.random() together with Math.floor() (or Math.trunc()) to generate random integers.
Use helper functions like getRandomInt(min, max) instead of repeating the same random-range logic everywhere.
Use Math.abs() to remove negative signs when you only care about magnitudes.
Always keep in mind that Math.random() is pseudo-random and not suitable for cryptographic purposes.

? Try It Yourself

Generate a random number between 50 and 100 using getRandomInt() or by writing the expression yourself.
Round 3.14159 using Math.round(), Math.floor(), and Math.ceil() and compare the results.
Use Math.max() and Math.min() to find the largest and smallest values from an array of numbers.
Write a function that simulates rolling two dice and returns their total.
Create a simple “random color picker” that changes the background color of the page using the colors array example.