I was working on the 1st lesson of the Javascript course and all was worked fine until I reach the Step 80: now I can’t “Check my code” and the preview doesn’t show anything…
Look for a vertical red line in the slider on the right. This indicates something is wrong in your code and it wont let you check it until you correct this. Move the slider down to the red line and look for the error such as an extra or missing ‘)’.