<div class="post-toc-block float-default with-border"> 
						<div class="post-toc-header">Table of Contents</div>
						<nav id="md-post-toc" class="md-post-toc"></nav>
						</div><p>Random numbers are essential in programming, whether you’re building games, simulations, quizzes, or generating unique identifiers. <a href="https://keploy.io/blog/community/javascript-array-filter-method-guide">JavaScript</a> provides built-in methods to create random numbers, integers, booleans, and even shuffle arrays. In this guide, we’ll cover everything from basic <strong>javascript random number</strong> to advanced randomization techniques, complete with code examples.</p>
<h2>Basics of Generating a Random Number in JavaScript</h2>
<p>In JavaScript, the primary method for generating random numbers is <code>Math.random()</code>. This method returns a floating-point random number between 0 (inclusive) and 1 (exclusive). This means it will return a value in the range [0, 1), like <code>0.2345</code> or <code>0.6789</code>. It’s as simple as that! Let’s check a code sample for this:</p>
<pre><code>javascript
let randomNum = Math.random();
console.log(randomNum); // Outputs a random number between 0 and 1</code></pre>
<p>This would give an output like this, if we ran the program on our systems:</p>
<p><img decoding="async" src="https://wp.keploy.io/wp-content/uploads/2024/11/a8b9e0ce-0d09-4adb-ad38-f0e667c9-1.webp" alt="output random" /></p>
<p>Although, this is a great starting point, but if we need a random integer or a number in a specific range, <code>Math.random()</code> alone won’t be enough to do the job.</p>
<h2>Generating Random Numbers in a Specific range</h2>
<p>To generate a random number in a specific range, say between a particular <code>min</code> value and another particular <code>max</code> value, you’ll need to do a bit of math. Here’s a formula that will help:</p>
<pre><code>javascript
function getRandomInRange(min, max) {
  return Math.random() * (max - min) + min;
}

console.log(getRandomInRange(10, 20)); // Outputs a number between 10 and 20</code></pre>
<p>This would give an output like:</p>
<p><img decoding="async" src="https://wp.keploy.io/wp-content/uploads/2024/11/31462bb9-e5ae-48b7-bb57-3eb5495e-1.webp" alt="output random" /></p>
<p>The <code>Math.random()</code> generates a number between 0 and 1. And, by multiplying it with <code>(max - min)</code> and then adding <code>min</code>, you ensure the number falls within the range <code>[min, max)</code>.</p>
<h2>Generating Random Integers in a Javascript</h2>
<p>Sometimes, you may need a whole number instead of a floating-point value. To generate random integers in a specific range, you can use <code>Math.floor()</code> or <code>Math.ceil()</code>. Let’s check how:</p>
<pre><code>javascript
function getRandomIntInRange(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

console.log(getRandomIntInRange(1, 100)); // Outputs a random integer between 1 and 100</code></pre>
<p>When we run this code, we will get a similar output like this:</p>
<p><img decoding="async" src="https://wp.keploy.io/wp-content/uploads/2024/11/run-code-output.webp" alt="run code output" /></p>
<p>Here, <code>Math.floor()</code> rounds down to the nearest integer, ensuring the result is an integer within the range <code>[min, max]</code>.</p>
<h2>Generating Random Booleans values</h2>
<p>You can also generate random boolean values (true or false) in JavaScript, which can be useful in games or in any scenario of decision-making:</p>
<pre><code>javascript
function getRandomBoolean() {
  return Math.random() &gt;= 0.5;
}

console.log(getRandomBoolean()); // Outputs true or false randomly</code></pre>
<p>We’ll get a similar output like this, when we will run the code:</p>
<p><img decoding="async" src="https://wp.keploy.io/wp-content/uploads/2024/11/ed23a257-5fc0-4ed9-b5dd-a80ce6cd-1.webp" alt="run code output" /></p>
<h2>Generating Random Values from an Array</h2>
<p>Now, if we want to select a random element from an array, we can easily use <code>Math.floor()</code> with <code>Math.random()</code>. Let’s see how we can do that:</p>
<pre><code>javascript
const colors = [&quot;red&quot;, &quot;green&quot;, &quot;blue&quot;, &quot;yellow&quot;];
const randomColor = colors[Math.floor(Math.random() * colors.length)];
console.log(randomColor); // Outputs a random color from the array</code></pre>
<p>Now, this will give us any random element from the array like this, when we run the program:</p>
<p><img decoding="async" src="https://wp.keploy.io/wp-content/uploads/2024/11/random-element.webp" alt="random element" /></p>
<h2>Shuffling an Array in Javascript</h2>
<p>To shuffle an array, i.e. randomly rearrange its elements, you can use the Fisher-Yates shuffle algorithm. Here’s how it can be implemented with the help of <code>Math.random()</code>:</p>
<pre><code>javascript
function shuffleArray(array) {
  for (let i = array.length - 1; i &gt; 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [array[i], array[j]] = [array[j], array[i]];
  }
  return array;
}

const numbers = [1, 2, 3, 4, 5];
console.log(shuffleArray(numbers)); // Outputs a shuffled array</code></pre>
<p>Now, when we’ll run the program, it will give us a shuffled array like this:</p>
<p><img decoding="async" src="https://wp.keploy.io/wp-content/uploads/2024/11/shuffled-array-output.webp" alt="shuffled array output" /></p>
<h2>Generating Random UUID Generation</h2>
<p>In a lot of development scenarios, you might need to use unique identifiers, and you might consider using a random UUID (Universally Unique Identifier). Here’s a basic example of a UUID generator using our <code>random</code> method:</p>
<pre><code>javascript
function generateUUID() {
  return &#039;xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx&#039;.replace(/[xy]/g, (c) =&gt; {
    const r = Math.random() * 16 | 0;
    const v = c === &#039;x&#039; ? r : (r &amp; 0x3 | 0x8);
    return v.toString(16);
  });
}

console.log(generateUUID()); // Outputs a random UUID</code></pre>
<p>So, when we run this program, it will generate a random UUID like this:</p>
<p><img decoding="async" src="https://wp.keploy.io/wp-content/uploads/2024/11/run-code-output2.webp" alt="run code output2" /></p>
<h2>Generating Cryptographically Secure Random Numbers</h2>
<p>While <code>Math.random()</code> works for most use cases, it is <strong>not suitable for cryptographic purposes</strong> like generating passwords, tokens, or secure keys because it’s predictable.</p>
<p>For security-critical applications, you should use the <strong>Web Cryptography API</strong>:</p>
<pre><code>javascript
function getSecureRandom() {
  const array = new Uint32Array(1);
  window.crypto.getRandomValues(array);
  return array[0];
}

console.log(getSecureRandom()); // Outputs a cryptographically secure random number</code></pre>
<p>Use <code>crypto.getRandomValues()</code> whenever you need unpredictable and secure randomness.</p>
<h2>Conclusion</h2>
<p>JavaScript offers a versatile set of tools for working with random numbers. From simple <code>Math.random()</code> calls to generating integers, booleans, shuffling arrays, or creating UUIDs, these techniques allow you to add unpredictability to your projects. Practice these methods in real-world scenarios like games, simulations, or random quizzes to truly master randomness in JavaScript.</p>
<h2>Further Readings</h2>
<p><a href="https://keploy.io/blog/technology/mastering-nyc-enhance-javascript-typescript-test-coverage">https://keploy.io/blog/technology/mastering-nyc-enhance-javascript-typescript-test-coverage</a></p>
<p><a href="https://keploy.io/blog/community/javascript-var-vs-let-vs-const">https://keploy.io/blog/community/javascript-var-vs-let-vs-const</a></p>
<h2>Frequently Asked Questions</h2>
<h3><strong>Is</strong> <code>Math.random()</code> <strong>truly random?</strong></h3>
<p>No, <code>Math.random()</code> is not truly random. It is a pseudo-random number generator (PRNG), which means it uses a deterministic algorithm to generate numbers. While these numbers may appear random, they are generated by a predictable process.</p>
<h3><strong>Can I set a seed for</strong> <code>Math.random()</code> <strong>in JavaScript?</strong></h3>
<p>JavaScript&#8217;s <code>Math.random()</code> does not allow you to set a seed natively. Some other programming languages allow seeded random number generators for reproducibility, but in JavaScript, you&#8217;ll need a third-party library (such as <code>seedrandom</code>) if you want this feature.</p>
<h3><strong>Why does</strong> <code>Math.random()</code> return a number between 0 and 1, instead of a larger range?</h3>
<p>The design choice behind <code>Math.random()</code> returning a floating-point number between 0 and 1 is to provide flexibility. By returning a normalized value, developers can easily scale it to any range or format, such as integers or numbers between a specific <code>min</code> and <code>max</code>.</p>
<h3><strong>Are there any performance concerns with using</strong> <code>Math.random()</code> frequently?</h3>
<p>In most cases, <code>Math.random()</code> is efficient and fast enough for regular use, such as in games, animations, or other everyday applications. However, if you need to generate millions of random numbers in real-time (for example, in high-performance simulations), you might want to consider optimized solutions like WebAssembly-based random generators or custom algorithms.</p>
<h3><strong>Can</strong> <code>Math.random()</code> be used for cryptographic purposes?</h3>
<p>No, <code>Math.random()</code> is not secure enough for cryptographic purposes. It is predictable and should not be used in situations that require secure random numbers, like generating passwords or cryptographic keys. For these scenarios, you should use the <code>crypto.getRandomValues()</code> method provided by the Web Cryptography API, which offers more secure randomness.</p>

         
        
                    

                    
                    <div class="pp-multiple-authors-boxes-wrapper pp-multiple-authors-wrapper pp-multiple-authors-layout-boxed multiple-authors-target-the-content box-post-id-16 box-instance-id-1 ppma_boxes_16"
                    data-post_id="16"
                    data-instance_id="1"
                    data-additional_class="pp-multiple-authors-layout-boxed.multiple-authors-target-the-content"
                    data-original_class="pp-multiple-authors-boxes-wrapper pp-multiple-authors-wrapper box-post-id-16 box-instance-id-1">
                                                                                    <h2 class="widget-title box-header-title">Author</h2>
                                                                            <span class="ppma-layout-prefix"></span>
                        <div class="ppma-author-category-wrap">
                                                                                                <span class="ppma-category-group ppma-category-group-">
                                                                                                                        <ul class="pp-multiple-authors-boxes-ul">
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            <li class="pp-multiple-authors-boxes-li author_index_0 author_swapnoneel-saha has-avatar">
                                                                                                                                                                                                                                            <div class="pp-author-boxes-avatar">
                                                                                                                                            <img alt='Swapnoneel Saha' src='https://wp.keploy.io/wp-content/uploads/2024/10/Swapnoneel-saha.jpeg' srcset='https://wp.keploy.io/wp-content/uploads/2024/10/Swapnoneel-saha.jpeg' class='multiple_authors_guest_author_avatar avatar' height='80' width='80'/>                                                                                                                                    </div>
                                                            
                                                            <div class="pp-author-boxes-avatar-details">
                                                                                                                                                                                                <div class="pp-author-boxes-name multiple-authors-name">
                                                                        <a href="https://wp.keploy.io/author/swapnoneel-saha/" rel="author" title="Swapnoneel Saha" class="author url fn">Swapnoneel Saha</a> 
                                                                    </div>
                                                                                                                                                                                                                                                                    <p class="pp-author-boxes-description multiple-authors-description">
                                                                        DevRel Engineer at Keploy 🐰 and Technical Writer at TutorialsPoint, with experience in full-stack development, UI/UX design, and Java/Python programming. Currently pursuing B.Tech in CSE from MAKAUT, I'm a 4x hackathon winner and passionate lifelong learner.                                                                    </p>
                                                                                                                                <a class="ppma-author-user_url-profile-data ppma-author-field-meta ppma-author-field-type-url" aria-label="Website" href="https://www.linkedin.com/in/swapnoneel-saha-14a3161b6/" rel="dofollow" target="_blank"><span class="dashicons dashicons-admin-links"></span> </a>
                                                                                                                                
                                                                                                                            </div>
                                                                                                                                                                                                                                                                                                                                                                                                             </li>
                                                                                                                                                                                                                                    </ul>
                                                                            </span>
                                                                                    </div>
                    <span class="ppma-layout-suffix"></span>
                    </div>
                    
                    
                
                                <style>
                .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .pp-author-boxes-avatar img { width: 80px !important; height: 80px !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .pp-author-boxes-avatar img { border-style: none !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .pp-author-boxes-avatar img { border-radius: 50% !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .pp-author-boxes-meta a { background-color: #655997 !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .pp-author-boxes-meta a { color: #ffffff !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .pp-author-boxes-meta a:hover { color: #ffffff !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .ppma-author-user_email-profile-data { background-color: #655997 !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .ppma-author-user_email-profile-data { border-radius: 100% !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .ppma-author-user_email-profile-data { color: #ffffff !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .ppma-author-user_url-profile-data { background-color: #655997 !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .ppma-author-user_url-profile-data { border-radius: 100% !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .ppma-author-user_url-profile-data { color: #ffffff !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .pp-author-boxes-recent-posts-title { border-bottom-style: dotted !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .pp-multiple-authors-boxes-li { border-style: solid !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .pp-multiple-authors-boxes-li { border-width: 1px !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .pp-multiple-authors-boxes-li { border-color: #999 !important; } .pp-multiple-authors-boxes-wrapper.box-post-id-16.pp-multiple-authors-layout-boxed.multiple-authors-target-the-content.box-instance-id-1 .pp-multiple-authors-boxes-li { color: #3c434a !important; }             </style>

How to Generate Random Numbers in JavaScript

Jest Mock: How to Mock a Provider in JavaScript Testing

TypeScript vs JavaScript : Choosing the Right One

React DevTools: Complete Guide for Modern Web Developers

Master JavaScript filter() Method: Guide with Examples

Angular vs React : Complete Guide for Development in 2025

What is Unit Testing?

Inside the Java Native Interface (JNI)

Building Keploy.io, an EBPF based open source framework to generate test cases and data stubs from API calls.

Neha Gupta

Cloud technology veteran and probably the youngest (globally) to have completed all 5 AWS certifications (including Solutions architect Professional and Dev­ops engineer professional)

How To Generate Random Numbers In Javascript

More Stories