I am a beginner and try to code a little game. I have already a counter which shows you the count/ score. I would like to add now a little Highscore for the gamesession. What do I have to add?

/* COUNTER */

var onclick = "stopSliding('slider".concat(counter, "','slider", counter+1, "','slider", counter-1, "')");
btn.setAttribute("onclick",onclick);
counter++;
scoreboard.innerHTML = "<p>DEIN SCORE IST <span id='scorecolor'>" + [counter-2] + "!</span></p>";
setRandomColor();