Guitar string strum

HTML

<canvas id="canvas"></canvas>

JavaScript

var c = document.getElementById("canvas");
var ctx = c.getContext("2d");
c.width = 300;
c.height = 100000;

var tremble = 2;

var myInterval;

function strum() {
    ctx.clearRect(0,0,c.width,c.height);
    
    drawString();
    
    ctx.beginPath();
    ctx.moveTo(0,50+tremble);
    ctx.lineTo(c.width,50+tremble);
    ctx.stroke();
    tremble*=-1;
}

function drawString() {
    ctx.beginPath();
    ctx.moveTo(0,50);
    ctx.lineTo(c.width,50);
    ctx.stroke();
}

drawString();

setTimeout(function() {
 myInterval = setInterval(strum,16);
    setTimeout(function() {
        clearInterval(myInterval);
        ctx.clearRect(0,0,c.width,c.height);
        drawString();        
    },500);
},2000);