Common usage of animation with callback called constantly

gistfile1.js

function animLoop( render, element ) {
    var running, lastFrame = +new Date;
    function loop( now ) {
        // stop the loop if render returned false
        if ( running !== false ) {
            requestAnimationFrame( loop, element );
            var deltaT = now - lastFrame;
            // do not render frame when deltaT is too high
            if ( deltaT < 160 ) {
                running = render( deltaT );
            }
            lastFrame = now;
        }
    }
    loop( lastFrame );
}
 
// Usage
animLoop(function( deltaT ) {
    elem.style.left = ( left += 10 * deltaT / 16 ) + "px";
    if ( left > 400 ) {
      return false;
    }
// optional 2nd arg: elem containing the animation
}, animWrapper );