Live Demo: JavaScript Function Declaration vs. Function Expression

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>JavaScript Function Declaration vs. Function Expression</title>
</head>
<body>
    <script>
    declaration(); // Prints: Hi, I'm a function declaration!
    function declaration() {
        document.write("Hi, I'm a function declaration!");
    }
     
    expression(); // Uncaught TypeError: undefined is not a function
    let expression = function() {
        document.write("Hi, I'm a function expression!");
    }
    </script>
</body>
</html>  