Live Demo: JavaScript Extract Fixed Number of Characters from a String

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>JavaScript Extract Fixed Number of Characters from a String</title>
</head>
<body>
    <script>
    let str = "The quick brown fox jumps over the lazy dog.";
    document.write(str.substr(4, 15) + "<br>"); // Prints: quick brown fox
    document.write(str.substr(-28, -19) + "<br>"); // Prints nothing
    document.write(str.substr(-28, 9) + "<br>"); // Prints: fox jumps
    document.write(str.substr(31)); // Prints: the lazy dog.
    </script>
</body>
</html>