A simple music tracker for patatap

patatap_tracker.js

// - Go to http://patatap.com/
// - open the developer console (note: F12 is disabled!, open with inspect)
// - execute this snippet
// - change 'seq' to change the note sequence. Keys must be uppercase
// - you can send 1 function instead of a note to control other stuff in the page

function keypress(char) {
    $.event.trigger({type: 'keydown', which: char.charCodeAt(0)})
}

function bpmToMillis() {
    return ((60 / bpm) * 1000) / subdivisions
}

async function tracker() {
    while (seq.length > 0) { // avoid freeze if emptying seq
        for (let notes of seq) {
            if (notes.length > 0 && typeof notes[0] === 'function') {
                notes[0]()
            } else {
                if (play) notes.forEach(keypress)
                await new Promise((resolve) =>
                    setTimeout(resolve, bpmToMillis())
                )
            }
        }
    }
}
var seq = [['a']]
var bpm = 120
var subdivisions = 2
var play = true

// create a textarea for pasting sequences
$('body').append('<textarea id="seq" style="position:absolute; width:30em; height: 40em; color: black">// paste your sequence and press enter\nseq = [\n["A"]\n]</textarea>')
$('#seq').on('keyup', (e) => {
    if(e.which == 13 && !e.shiftKey && !e.altKey && !e.ctrlKey && !e.metaKey) {
        eval(e.target.value)
        e.target.style.width = '20px'
        e.target.style.height = '20px'
    }
    return e
})

tracker()

// sample sequence :)
seq = [
    ['A'], // single note
    [], // send no notes to just pass a subdivision
    ['D'],
    ['A', 'P'], // multiple notes at the same time
    [],
    ['D'],
    [],
    ['E', 'O'],
    [],
    ['A'],
    [],
    ['D'],
    ['K'],
    ['A'],
    [],
    ['D'],
    [],
    ['E'],
    [],
    ['A'],
    ['I'],
    ['D'],
    [],
    ['A'],
    ['I'],
    ['D', 'K'],
    [],
    ['E', 'N'],
    [],
    ['A', 'C'],
    [],
    ['D', 'N'],
    [],
    ['E', 'U', 'D', 'E', 'S'],
    [],
    ['G', 'O'],
    [],
    [() => {bpm+=40; console.log(`Up we go. BPM: ${bpm}`)}], // you can send functions too. These don't count as a beat.
]