var bend = -10;
    var path = document.getElementById("line-path");

    var x = 10;
    var swing = 52;
    var friction = .99;

    function step() {
        x++;


        swing *= friction;

        bend = (10 * Math.sin(x/5) * swing);
       
        var px= 0,py=0;

        if (bend.toFixed(2) == 0) bend = 0.01;      
        var pathData = "M 150 " + px  + "C -350 40 ,0 " + bend.toFixed(3) + ", 150 " + py;

        path.setAttribute("d", pathData);


        window.requestAnimationFrame(step);
    }

    path.onclick=function(e) {
        var offset = e.clientX / window.innerWidth - 0.5;
        swing+=70;
    }


    window.requestAnimationFrame(step);