Move Div Element HTML JavaScript Keypress

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>JavaScript Key Press Move Div</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <style>
      #sprite{
        background:blue;
        width:50px;
        height:50px;
        position: relative;
        left: 10px;
      }
    </style>
    <script>
      //wait for document to load
      document.addEventListener("DOMContentLoaded", function(){
        let sprite = document.querySelector("#sprite");
        sprite.pos = 0;
        sprite.speed = 10;
        sprite.mleft = false;
        sprite.mright = false;
      });

      document.addEventListener('keydown', function( ev ) {
        if(ev.key == "ArrowRight"){ sprite.mright = true; }
        if(ev.key == "ArrowLeft"){ sprite.mleft = true; }
      });

      document.addEventListener('keyup', function( ev ) {
        if(ev.key == "ArrowRight"){ sprite.mright = false; }
        if(ev.key == "ArrowLeft"){ sprite.mleft = false; }
      });

      //Main Game Loop
      setInterval(function(){
        if ( sprite.mleft ){ sprite.pos -= sprite.speed; }
        if ( sprite.mright ){ sprite.pos += sprite.speed; }
        sprite.style.left = sprite.pos + "px";
      },10);
    </script>
  </head>
  <body>
    <div id="sprite"></div>
  </body>
</html>