Fundamentals_JS/JsFunctions.html at main · Sparky-code/Fundamentals_JS · GitHub

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<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8">
        <Title> Javascript.info/function-basics</Title>
    </head>
    <body>
        <script>

            /*

            // Function Declaration

            function showMessage() { // function name(parameter1, paramenterN) {
                alert ('Hello world!'); //    ...body...
            }

            showMessage();
            showMessage();

            // Local Variables

            function showMessage() {
              let message = 'Hello, I\'m JavaScript!';

              alert( message);
            }

            showMessage(); // Hello, I'm JavaScript!

            alert( message ); // <-- Error! the variable is local to the function

            */
           /*

            // Outer Variables

            let userName = 'John';

            function showMessage() {
                let message = 'Hello, ' + userName;
                alert(message);
            }
            showMessage(); // Hello, John
            // function has full access to outer variables, which it can modify as well

            */

            /*

            let userName = 'John';

            function showMessage() {
                userName = 'Bob'; //(1) changed the outer variable

                let message = 'Hello, ' + userName;
                alert(message);
            }

            alert(userName); // John, before function call

            showMessage();

            alert (userName); // Bob, modified by function

            // variables declared outside of functions, such as the outer userName, are 'Global'.
            // Global variables are visible from ANY fuction (unless shadowed by locals)
            // Min the use of global variables, primary for project level-data if at all
            // Modern code has few/no globals

            /*

            // Parameters -- Pass arbitrary data to functions

            function showMessage(from, text) {
                alert (from + ': ' + text);
            }

            showMessage('Ann', 'Hello!'); // Ann: Hello! (*)
            showMessage('Ann', 'What\'s up?'); // Ann: What's up? (*)

            // given values (*, **) are copied to local variables [from, text] --> function then uses them

            */

            /*

            // Parameters 2

            function showMessage(from, text) {

                from = '*' + from + '*'; //makes "from" look nicer

                alert (from + ': ' + text);
            }

            let from = "Ann";

            showMessage(from, "Hello"); // *Ann*: Hello

            // value of "from" remains unchanged, function modifies a local copy
            alert (from); // Ann

            // values as function parameters also called arguments
            // parameter = variable listed inside the () in the function declar (decl time term)
            // argument = value passed to the function when called (call time function)
            // declare functions with listed params, call them by passing arguments

            */

            /*

            // Default Values

            // when values are not defined, default values (undefined, or user set) will return
            // Ex 1 showMessage(from, text) as above > *Ann*: undefined since a value for text was not passed

            function showMessage(from, text = 'no text given') {
                alert( from + ': ' + text );
            }

            showMessage('Ann'); // Ann: no text given

            // 'no text given' is passed as a string but more complex series are also possible
            //Ex 2

            // function showMessage(from, text = anotherFunction()) {
                //anotherFunction() on executes if no text is given > result populates the value of text

            */

            /*

            // Alt default params

            function showMessage(text) {
                // ..

                if (text === undefined) { // if param is missing
                    text = 'empty message';
                }

                alert(text);
            }

            showMessage(); // empty message

            */

            /*

            //alt || operator

            function showMessage(text) {
                // if text is undef. or otherwise falsy, set it to 'empty'
                text = text || 'empty';
            }

            */

            /*

            // modern JS engines support nullish coalescing operator ?? > better when most falsy values such as 0 should be considered 'normal'

            function showCount(count) {
                // if count is undefined or null, show 'unknown'
                alert(count ?? 'unknown')
            }

            showCount(0); // 0
            showCount(null); // unknown
            showCount(); //unknown

            */

            /*

            // Return values back into the calling code

            function sum(a, b) {
                return a +b;
            }

            let result = sum(1, 2);
            alert( result ); // 3

            */

            /*

            function checkAge(age) {
                if (age >= 18) {
                    return true;
                } else {
                    return confirm('Do you have parental permission to continue?');
                }
            }


            let age = prompt('How old are you?', 18);

            if (checkAge(age) ) {
                alert( 'Access Granted' );
            } else {
                alert( 'Access Denied');
            }

            // no input still returns 'Do you have permission...?'


            // THis doesnt actually work... Idk
            // supposed to represent this:
            // Using return without a value, causing the function to exit imeediately

            function showMovie(age) {
                if ( !checkAge(age) ) {
                    return;
                }
                alert ('Now Playing'); // (*)
            }

            */

            /*

            function doNothing() {
                return;
            }

            alert( doNothing() ===undefined); // true

            //an empty return is same as return undefined

            */

            /*

           // return
            //  (some + thing + helllla + long *f(a) + f(b))

            // !! dont do this - JS sees this as an empty return

            return (
              some + thing + helllla
               + long *f(a) + f(b)
            )

            // Do this instead

            */

            //Naming a function

            // should usually be a verb, concise, accurate, and descriptive
            // how would a stranger read it?
            // eg. get...returns a function
            // calc...calculate someting
            // create...create something
            // check... check something and return a boolean

            /*

            showMessage(...)  // Shows a message
            getAge(...) // returns the age (gets somehow)
            calcSum(...) // calculates a sum and returns result
            createForm(...) // creates a form (usually returns it)
            checkPermission(...) // checks a permission, returns true/false

            */

            // Functions == Comments
            // a large function is often best split into multiple smaller functions
            // this makes functions easier to debug and test
            // additionally this makes the function a great comment in itself
            //Ex

            /*

            function showPrimes(n) {

                for (let i = 2; i < n; i++) {
                    if (!isPrime(i)) continue;

                 alert( i ); // a prime
              }
            }

            function isPrime(n) {
              for (let i = 2; i < n; i++) {
                if ( n % i == 0) return false;
              }
              return true;
            }

        */

        /*
        function checkAge(age) {
            (age > 18 ? true : confirm('Did parents allow?'));
        }

        */

        /*

        function checkAge(age) {
            return (age > 18) || confirm('Did parents allow?');
        }

        */

        /*

        // My attempt - write a min(a, b) functionn

        function minValue(a, b) {
            let c = Math.min(a, b);
            alert(c);
        }

        // Solution 1 with 'if'

        function min(a, b) {
            if (a < b) {
                return a;
            } else {
                return b;
            }
        }

        // Solution 2 with '?'

        function min (a, b) {
            return a < b ? a : b;
        }

        */

        // My attempt - Write a function pow(x, n) **X to the power of N

        function pow(x, n) {
            return x **= n
        }

        // added to my solution based on solution below (input and display)

        let x = prompt('x?', '')
        let n = prompt('n?', '')
        alert(pow(x, n))

        /*

        // solution, drawn out to show looping it seems

        function pow(x, n) {
          let result = x;

          for (let i = 1; i < n; i++) {
            result *= x;
        }

          return result;
        }

        let x = prompt("x?", '');
        let n = prompt("n?", '');

        if (n < 1) {
          alert(`Power ${n} is not supported, use a positive integer`);
        } else {
          alert( pow(x, n) );
        }

        */


        </script>
    </body>
</html>