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abridged_keyboard_musical_instrument.js
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abridged_keyboard_musical_instrument.js
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/**
* file: abridged_keyboard_musical_instrument.js
* type: JavaScript
* author: karbytes
* date: 13_SEPTEMBER_2024
* license: PUBLIC_DOMAIN
*/
// Declare an audio context variable (which is a global program variable).
let audioContext = new (window.AudioContext || window.webkitAudioContext)();
/**
* Define a global variable which is an (immutable) dictionary populated by key-value pairs (i.e. definitions)
* where each key is the literal label of a computer keyboard key and where each value is the respective key's uniquely
* corresponding sound wave frequency requency (in terms of sound wave oscillations per second
* (i.e. hertz (abbreviated as Hz))).
*
* Each key-value pair in that dictionary is listed in ascending order in terms of sound wave frequency.
*
* The musical note associated with each of those sound wave frequencies is denoted by that sound wave
* frequency's uniquely corresponding musical note comment.
*/
const noteFrequencies = {
'z': 130.81, // C3
'x': 146.83, // D3
'c': 164.81, // E3
'v': 174.61, // F3
'b': 196.00, // G3
'n': 220.00, // A3
'm': 246.94, // B3
',': 261.63, // C4 (Middle C)
'.': 293.66, // D4
'/': 329.63, // E4
'a': 349.23, // F4
's': 392.00, // G4
'd': 440.00, // A4
'f': 493.88, // B4
'g': 523.25, // C5
'h': 587.33, // D5
'j': 659.25, // E5
'k': 698.46, // F5
'l': 783.99, // G5
';': 880.00, // A5
'q': 987.77, // B5
'w': 1046.50, // C6
};
// Define a global variable which represents the HTML element whose identifier (id) is "keyboard" on the web page named abridged_keyboard_musical_instrument.
const keyboardDiv = document.getElementById('keyboard');
/**
* Return a String type value which describes the number of milliseconds which have elapsed since the Unix Epoch.
*
* Note that the Unix Epoch is 01_JANUARY_1970 at 0 hours, 0 minutes, 0 seconds, and 0 seconds
* (i.e. 00:00:00) (i.e. midnight) (Coordinated Universal Time (UTC)).
*
* @return {String} text which denotes the number of milliseconds which have elapsed since the Unix Epoch.
*/
function generate_time_stamp() {
const milliseconds_elapsed_since_unix_epoch = Date.now();
return milliseconds_elapsed_since_unix_epoch + " milliseconds since midnight on 01_JANUARY_1970.";
}
/**
* Return a String type value which is used to instantiate a paragraph type web page element such that
* the String type value which is passed into this function as its only input is that paragraph element's
* inner HTML content.
*
* Note that the String type constant variable values are broken up into single-character String type values
* to avoid causing the WordPress web page editor to interpret HTML tags in the web page body with
* source code which is hosted on that web page inside of PRE (preformatted) web page elements.
*
* @param {String} inner_HTML is assumed to be plain text or HTML content.
*
* @return {String} a sequence of text characters which is used to instantiate a paragraph (P) web page element.
*/
function generate_paragraph_html_element(inner_html) {
const opening_paragraph_tag = ('<' + 'p' + '>'), closing_paragraph_tag = ('<' + '/' + 'p' + '>');
try {
if (typeof inner_html.length !== "number") throw 'The expression (typeof inner_html.length !== "number") was evaluated to be true.';
return opening_paragraph_tag + inner_html + closing_paragraph_tag;
}
catch(exception) {
console.log("An exception to normal functioning occurred during the runtime of generate_paragraph_html_element(inner_html): " + exception);
}
}
/**
* Respond to the event of the web page named abridged_keyboard_musical_instrument.html being loaded by a web browser.
*
* This function prints a time-stamped message indicating when the web page was last
* loaded by the web browser in a DIV element on that web page whose identifier is "console".
*
* This function also initializes the audio context (which works offline and which utilizes the
* web browser's built-in sound-generating capabilities which correspond with the local machine's
* operating system (to control the hardware which causes sound waves to be emitted from the machine)).
*
* Assume that all three files which constitute this single web page application are located
* in the same local file directory (and those file are
* karbytes_aesthetic.css,
* abridged_keyboard_musical_instrument.js, and
* abridged_keyboard_musical_instrument.html).
*/
function initialize_application() {
// Initialize variables which are local to this function.
let time_stamped_message = "";
// Execute a try-catch block. If runtime exceptions are found, exit the try block and print an error message to the web browser console.
try {
// If the audio context has not already been defined, then define it now.
if (!audioContext) audioContext = new (window.AudioContext || window.webkitAudioContext)();
// Populate the div whose identifier is "console" with a time stamped message indicating that this function was called (and when it was called).
time_stamped_message = ("The function named initialize_application() was called at time: " + generate_time_stamp());
console.log(time_stamped_message);
time_stamped_message = generate_paragraph_html_element(time_stamped_message);
console_div = document.getElementById("console");
console_div.innerHTML = time_stamped_message;
}
catch(exception) {
console.log("An exception to normal functioning occurred during the runtime of initialize_application(): " + exception);
}
}
/**
* This function to dynamically instantiates each piano key in the piano user interface (UI) on the corresponding web page
* (i.e. abridged_keyboard_musical_instrument.html).
*
* Specifically, this function populates the HTML element whose identifier (id) is "keyboard" with the following labeled keyboard keys
* (where each key represents a uniquely corresponding sound wave frequency (in terms of sound wave oscillations per second
* (i.e. hertz (abbreviated as Hz))) and the musical note name of each of that particular frequency):
* 'z' // 130.81 Hz (C3)
* 'x' // 146.83 Hz (D3)
* 'c' // 164.81 Hz (E3)
* 'v' // 174.61 Hz (F3)
* 'b' // 196.00 Hz (G3)
* 'n' // 220.00 Hz (A3)
* 'm' // 246.94 Hz (B3)
* ',' // 261.63 Hz (C4 (Middle C))
* '.' // 293.66 Hz (D4)
* '/' // 329.63 Hz (E4)
* 'a' // 349.23 Hz (F4)
* 's' // 392.00 Hz (G4)
* 'd' // 440.00 Hz (A4)
* 'f' // 493.88 Hz (B4)
* 'g' // 523.25 Hz (C5)
* 'h' // 587.33 Hz (D5)
* 'j' // 659.25 Hz (E5)
* 'k' // 698.46 Hz (F5)
* 'l' // 783.99 Hz (G5)
* ';' // 880.00 Hz (A5)
* 'q' // 987.77 Hz (B5)
* 'w' // 1046.50 Hz (C6)
*/
function createKeyUI(key) {
try {
const keyDiv = document.createElement('div');
keyDiv.classList.add('key');
keyDiv.textContent = key.toUpperCase();
keyDiv.id = key;
keyboardDiv.appendChild(keyDiv);
}
catch(exception) {
console.log("An exception to normal functioning occurred during the runtime of createKeyUI(key): " + exception);
}
}
/**
* This function adds keys to the keyboard DIV in ascending note order.
*/
Object.keys(noteFrequencies).forEach(createKeyUI);
/**
* This function generates physical sound waves whose frequencies are the values input by this function.
*
* This function also prints a time-stamped message indicating when a UI keyboard key was
* most recently pressed in the "console" DIV.
*/
function playNote(frequency) {
let time_stamped_message = "";
try {
const oscillator = audioContext.createOscillator();
const gainNode = audioContext.createGain();
oscillator.type = 'sine';
oscillator.frequency.setValueAtTime(frequency, audioContext.currentTime);
gainNode.gain.setValueAtTime(0.5, audioContext.currentTime);
oscillator.connect(gainNode);
gainNode.connect(audioContext.destination);
oscillator.start();
oscillator.stop(audioContext.currentTime + 0.5); // Stop playing the note after 0.5 seconds elapses.
// Append the text in the div whose identifier is "console" with a time stamped message indicating that this function was called (and when it was called).
time_stamped_message = ("The function named playNote(frequency) (where frequency = " + frequency + ") was called at time: " + generate_time_stamp());
console.log(time_stamped_message);
time_stamped_message = generate_paragraph_html_element(time_stamped_message);
console_div = document.getElementById("console");
console_div.innerHTML += time_stamped_message;
}
catch(exception) {
console.log("An exception to normal functioning occurred during the runtime of playNote(frequency): " + exception);
}
}
/**
* This function responds to the event of a UI keyboard key being pressed.
*/
document.addEventListener('keydown', (event) => {
const key = event.key.toLowerCase();
if (noteFrequencies[key]) {
playNote(noteFrequencies[key]);
// Add visual feedback to the key (by changing the background color of the corresponding key).
const keyDiv = document.getElementById(key);
if (keyDiv) {
keyDiv.classList.add('pressed');
}
}
});
/**
* This function responds to the event of a UI keyboard key being unpressed.
* Specifically, this function changes the background color of the respective key back to light gray
* (after temporarily being set to green (for 0.5 seconds)).
*/
document.addEventListener('keyup', (event) => {
const key = event.key.toLowerCase();
const keyDiv = document.getElementById(key);
if (keyDiv) {
keyDiv.classList.remove('pressed');
}
});