JavaScript Random Number Generator

Instantly generate secure, customizable random numbers for browsers & Node.js. Try our javascript code generator tools for more options.

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Random Number Generator

Code Examples

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

// Generate random float between min and max
function getRandomFloat(min, max, decimals = 2) {
  const random = Math.random() * (max - min) + min;
  return parseFloat(random.toFixed(decimals));
}

// Generate array of random numbers
function generateRandomArray(min, max, count, allowDuplicates = true) {
  const numbers = [];
  const used = new Set();
  
  for (let i = 0; i < count; i++) {
    let number = getRandomInt(min, max);
    
    if (!allowDuplicates) {
      while (used.has(number)) {
        number = getRandomInt(min, max);
      }
      used.add(number);
    }
    
    numbers.push(number);
  }
  
  return numbers;
}

// Usage examples
console.log(getRandomInt(1, 100)); // Random integer 1-100
console.log(getRandomFloat(0, 1, 3)); // Random float 0-1 with 3 decimals
console.log(generateRandomArray(1, 10, 5, false)); // 5 unique numbers 1-10

Usage Tips:

  • • Use Math.random() for general purposes
  • • Use crypto.getRandomValues() for security-critical applications
  • • Always check for duplicates when generating unique numbers
  • • Consider performance when generating large arrays

💡 If the copy button doesn't work, you can click on the code area to select all, then press Ctrl+C (Windows) or Cmd+C (Mac) to copy manually

Common Use Cases

Game Development

Dice rolls, card shuffling, random events, loot drops

Roll a 6-sided die: getRandomInt(1, 6)
Shuffle cards: generateRandomArray(1, 52, 52, false)
Random enemy spawn: getRandomInt(1, 10)

Testing & Mock Data

Generate test data, simulate user behavior, performance testing

Mock user IDs: generateRandomArray(1000, 9999, 100)
Test scores: getRandomFloat(0, 100, 1)
Random timestamps: Date.now() + getRandomInt(0, 86400000)

Security Applications

Password generation, encryption keys, secure tokens

Generate PIN: getRandomInt(1000, 9999)
Random password: generateRandomString(8, 16)
Session tokens: crypto.randomUUID()

UI/UX Design

Random colors, animations, layout variations

Random color: #${getRandomInt(0, 16777215).toString(16)}
Animation delay: getRandomFloat(0, 2, 2)
Random avatar: getRandomInt(1, 10)

Data Analysis

Sample data, statistical analysis, A/B testing

Random sample: generateRandomArray(1, 1000, 100, false)
Normal distribution: generateNormalDistribution(0, 1, 1000)
A/B test groups: getRandomInt(1, 2) === 1 ? "A" : "B"

Quick Examples

🎲 Dice Roll

Math.floor(Math.random() * 6) + 1

🎨 Random Color

'#' + Math.floor(Math.random()*16777215).toString(16)

📊 Random Array

Array.from({length: 10}, () => Math.floor(Math.random() * 100))

🔐 Random Password

Math.random().toString(36).substring(2, 15)

Algorithm Comparison

Math.random()

Speed: ⚡⚡⚡Security: ❌

Built-in JavaScript random number generator

Use Case:
Games, animations, general purpose
Code Example:
Math.floor(Math.random() * (max - min + 1)) + min
Pros:
  • • Fast
  • • Simple to use
  • • Built-in
Cons:
  • • Not cryptographically secure
  • • Predictable
  • • Not suitable for security

crypto.getRandomValues()

Speed: ⚡⚡Security: ✅

Cryptographically secure random number generator

Use Case:
Passwords, tokens, security-critical applications
Code Example:
crypto.getRandomValues(new Uint32Array(1))[0] / (0xffffffff + 1)
Pros:
  • • Cryptographically secure
  • • Unpredictable
  • • Suitable for security
Cons:
  • • Slower
  • • More complex
  • • Not available in all environments

Seeded Random

Speed: ⚡⚡⚡Security: ⚠️

Deterministic random number generator with seed

Use Case:
Testing, reproducible results, simulations
Code Example:
seed = (seed * 9301 + 49297) % 233280; return seed / 233280;
Pros:
  • • Reproducible
  • • Fast
  • • Good for testing
Cons:
  • • Predictable
  • • Not secure
  • • Limited randomness

Detailed Comparison

AlgorithmSpeedSecurityComplexityBest For
Math.random()
Built-in JavaScript random number generator
⚡⚡⚡❌⭐Games, animations, general purpose
crypto.getRandomValues()
Cryptographically secure random number generator
⚡⚡✅⭐⭐Passwords, tokens, security-critical applications
Seeded Random
Deterministic random number generator with seed
⚡⚡⚡⚠️⭐⭐Testing, reproducible results, simulations

When to Use Which Algorithm?

Performance First

Use Math.random() for games, animations, and non-security applications where speed matters.

Security Critical

Use crypto.getRandomValues() for passwords, tokens, and any security-sensitive operations.

Testing & Debugging

Use seeded random generators for reproducible tests and debugging scenarios.

Best Practices

Use crypto.getRandomValues() for security

When generating passwords, tokens, or any security-critical data, always use the Web Crypto API.

// Good - Secure random number
const secureRandom = crypto.getRandomValues(new Uint32Array(1))[0] / (0xffffffff + 1);

// Bad - Predictable random number
const predictableRandom = Math.random();

Handle edge cases properly

Always validate input parameters and handle edge cases like min > max.

// Good - Handle edge cases
function getRandomInt(min, max) {
  if (min > max) [min, max] = [max, min];
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

Avoid Math.random() for security

Math.random() is not cryptographically secure and can be predicted.

// Warning - Not secure for passwords
const password = Math.random().toString(36).substring(2, 15);

// Better - Use crypto API
const password = crypto.getRandomValues(new Uint8Array(8))
  .reduce((str, byte) => str + byte.toString(16).padStart(2, '0'), '');

Consider performance for large arrays

When generating large arrays of unique numbers, use efficient algorithms.

// Efficient - Fisher-Yates shuffle
function generateUniqueArray(min, max, count) {
  const numbers = Array.from({length: max - min + 1}, (_, i) => min + i);
  for (let i = numbers.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [numbers[i], numbers[j]] = [numbers[j], numbers[i]];
  }
  return numbers.slice(0, count);
}

Use appropriate data types

Choose integer or float based on your needs, and specify decimal places for floats.

// Good - Specify decimal places
function getRandomFloat(min, max, decimals = 2) {
  const random = Math.random() * (max - min) + min;
  return parseFloat(random.toFixed(decimals));
}

Don't use random for IDs

Random numbers are not suitable for generating unique IDs. Use UUID or timestamp-based IDs.

// Bad - Random ID (can collide)
const id = Math.floor(Math.random() * 1000000);

// Good - Use UUID
const id = crypto.randomUUID();

// Good - Timestamp-based ID
const id = Date.now().toString(36) + Math.random().toString(36).substr(2);

Performance Tips

For Small Arrays (< 100 items)

  • • Use simple loops with duplicate checking
  • • Math.random() is fast enough
  • • No need for complex algorithms

For Large Arrays (> 1000 items)

  • • Use Fisher-Yates shuffle algorithm
  • • Pre-generate the full range
  • • Consider using Web Workers for UI responsiveness

Browser Compatibility

FeatureChromeFirefoxSafariEdge
Math.random()✅✅✅✅
crypto.getRandomValues()✅✅✅✅
crypto.randomUUID()✅✅⚠️ 15+✅

Frequently Asked Questions

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