Program to demonstrate function that will print hello in alert dialog box

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function showMessage() {
  alert( 'Hello everyone!' );
}
showMessage();
    </script>
</body>
</html>
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Program to demonstrate functions with parameters or arguments

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function showMessage(from, text) { // parameters: from, text
  alert(from + ': ' + text);
}

showMessage('Ann', 'Hello!'); // Ann: Hello! (*)
showMessage('Ann', "What's up?"); // Ann: What's up? (**)
    </script>
</body>
</html>

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Program to demonstrate a function that returns a value

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function sum(a, b) {
  return a + b;
}

let result = sum(1, 2);
alert( result ); // 3
    </script>
</body>
</html>

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Program to check for number of arguments to a function

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function f1(a) {}
function f2(a, b) {}
function many(a, b, ...more) {}

alert(f1.length); // 1
alert(f2.length); // 2
alert(many.length); // 2
    </script>
</body>
</html>

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program to demonstrate function expressions

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function sayHi() {   // (1) create
  alert( "Hello" );
}

let func = sayHi;    // (2) copy

func(); // Hello     // (3) run the copy (it works)!
sayHi(); // Hello    //     this still works too (why wouldn't it)
    </script>
</body>
</html>

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Program to demonstrate setTimeout function

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function sayHi() {
  alert('Hello');
}

setTimeout(sayHi, 1000);
    </script>
</body>
</html>

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Program to demonstrate setInterval function

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        // repeat with the interval of 2 seconds
let timerId = setInterval(() => alert('tick'), 2000);
    </script>
</body>
</html>

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