Live Demo: JavaScript Adding Numbers and Strings

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>JavaScript Adding Numbers and Strings</title>
</head>
<body>
    <script>
    // Creating variables
    let x = 10;
    let y = 20;
    let z = "30";
    
    // Adding a number with a number, the result will be sum of numbers
    document.write(x + y); // 30
    document.write("<br>");
    
    // Adding a string with a string, the result will be string concatenation
    document.write(z + z); // '3030'
    document.write("<br>");
    
    // Adding a number with a string, the result will be string concatenation
    document.write(x + z); // '1030'
    document.write("<br>");
    
    // Adding a string with a number, the result will be string concatenation
    document.write(z + x); // '3010'
    document.write("<br>");
    
    // Adding strings and numbers, the result will be string concatenation
    document.write("The result is: " + x + y); // 'The result is: 1020'
    document.write("<br>");
    
    // Adding numbers and strings, calculation performed from left to right
    document.write(x + y + z); // 'The result is: 3030'
    </script>
</body>
</html>