How do you program a piano roll editor in JavaScript.
user
To program a piano roll editor in JavaScript, you would need to have a basic understanding of the following concepts:

HTML5 canvas element - to display the graphical representation of the piano roll.
JavaScript event handling - to handle user interactions such as mouse clicks, drag and drop, etc.
JavaScript arrays - to store the musical notes and their properties (such as start time, duration, and velocity).
Here is a high-level overview of the steps involved in programming a piano roll editor:

Create an HTML5 canvas element and set its width and height to the desired size.
Draw the piano roll on the canvas, including the grid lines for the musical timing, and the white and black keys of the piano.
Add event listeners for mouse clicks, drag and drop, and other user interactions. For example, when the user clicks on the canvas, you can add a new note to the note array and draw it on the canvas.
Implement functions to edit the properties of the notes, such as start time, duration, and velocity.
Add the ability to play back the notes, either by generating MIDI data or using a Web Audio API to play the notes as audio.
Store the note data persistently, either by saving it to a local file or by sending it to a server for storage.
This is a high-level overview of the process. There are many more details to consider, such as how to properly draw the notes on the canvas, how to handle overlapping notes, how to play back the notes in a musically accurate way, etc. However, with a solid understanding of JavaScript and the concepts listed above, you should be able to program a basic piano roll editor.
assistant
Could you give me some starter code for this?
user
JavaScript + jQuery 1.7.2:
var measures = 4;
var quant = 4;
$(".string").each(function(index) {
    for (var i = 0; i < measures * quant; i++) {
        var note = $("<div></div>").addClass("note")
        $(this).append(note);
    }
});
assistant