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                <div id="frame">
  <div id="block"></div>


                #frame {
  border: 1px solid red;

#block {
  width: 20px;
  height: 40px;
  background: red;
  position: relative;


                // Move the block to the right, all the way to the end of the frame
const moveBlock = () => {
  // Convert the left position of the block (value of the form "XXpx") to a number
  const xBlock = parseFloat(getComputedStyle(blockElement).left);
  // Convert the width of the frame (value of the form "XXpx") to a number
  const xMax = parseFloat(getComputedStyle(frame).width);
  // If the block isn't already to the end of the frame
  if (xBlock + blockWidth <= xMax) {
    // Block movement = (xBlock + movement) + "px";
    animationId = requestAnimationFrame(moveBlock);
  else {
    // Cancel the animation

//const frameElement = document.getElementById("frame");
const blockElement = document.getElementById("block");
// Convert the block width (value of the form "XXpx") to a number
const blockWidth = parseFloat(getComputedStyle(block).width);

// Movement value in pixels
const movement = 7;

// Start the animation
let animationId = requestAnimationFrame(moveBlock);