Audio visual equalizer

Halo semuanya saya masih agak bingung dengan javascript. bisa tolong dibetulkan kodenya, saya mau buat tanpa input file sedangkan kode ini hanya berfungsi jika udah input file. mohon bantuannya.

window.onload = function() {

  var file = document.getElementById("thefile");
  var audio = document.getElementById("audio");

  file.onchange = function() {
    var files = this.files;
    audio.src = URL.createObjectURL(files[0]);
    audio.load();
    audio.play();
    var context = new AudioContext();
    var src = context.createMediaElementSource(audio);
    var analyser = context.createAnalyser();

    var canvas = document.getElementById("canvas");
    canvas.width = window.innerWidth;
    canvas.height = window.innerHeight;
    var ctx = canvas.getContext("2d");

    src.connect(analyser);
    analyser.connect(context.destination);

    analyser.fftSize = 256;

    var bufferLength = analyser.frequencyBinCount;
    console.log(bufferLength);

    var dataArray = new Uint8Array(bufferLength);

    var WIDTH = canvas.width;
    var HEIGHT = canvas.height;

    var barWidth = (WIDTH / bufferLength) * 6;
    var barHeight;
    var x = 0;

    function renderFrame() {
      requestAnimationFrame(renderFrame);

      x = 0;

      analyser.getByteFrequencyData(dataArray);

      ctx.fillStyle = "#000";
      ctx.fillRect(0, 0, WIDTH, HEIGHT);

      for (var i = 0; i < bufferLength; i++) {
        barHeight = dataArray[i];

        var r = barHeight + (25 * (i/bufferLength));
        var g = 250 * (i/bufferLength);
        var b = 50;

        ctx.fillStyle = "rgb(" + r + "," + g + "," + b + ")";
        ctx.fillRect(x, HEIGHT - barHeight, barWidth, barHeight);

        x += barWidth + 1;
      }
    }

    audio.play();
    renderFrame();
  };
};