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JavaScript Random

JavaScript's Math.random() generates a pseudo-random number between 0 (inclusive) and 1 (exclusive). By manipulating this value, you can generate random integers or select random items from arrays.

Key Topics

Basic Random

Math.random() returns a floating-point number from 0 up to but not including 1.

let randomNum = Math.random();
console.log(randomNum);

Output

> A number like 0.123456789 (varies each run)

Explanation: The exact output varies, but it will always be between 0 and 1.

Random in a Range

You can multiply and floor the result to get integers within a specific range.

function getRandomInt(max) {
    return Math.floor(Math.random() * max);
}
console.log(getRandomInt(10));

Output

> An integer between 0 and 9

Explanation: Multiplying by max and flooring truncates to a whole number within [0, max-1].

JavaScript Usage in DOM

This example shows how to generate a random number and display it on the webpage.

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Random in DOM</title>
</head>
<body>
    <h1>Random Number Demo</h1>
    <button onclick="showRandom()">Show Random Number</button>
    <p id="display"></p>

    <script>
        function showRandom() {
            let num = Math.floor(Math.random() * 100);
            document.getElementById("display").textContent = "Random: " + num;
        }
    </script>
</body>
</html>

Key Takeaways

  • Math.random(): Generates a number in [0,1).
  • Scaling and Flooring: Multiply and use Math.floor() for integer ranges.
  • DOM Integration: Display random results interactively on webpages.
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