Right now we use codemirror's JavaScript mode on the website but there's a JSX mode now so we should start using that instead.

if (widget.noHScroll) {
      (wrap.alignable || (wrap.alignable = [])).push(node);
      var width = dims.wrapperWidth;
      node.style.left = dims.fixedPos + "px";
      if (!widget.coverGutter) {
        width -= dims.gutterTotalWidth;
        node.style.paddingLeft = dims.gutterTotalWidth + "px";
      }
      node.style.width = width + "px";
    }
    if (widget.coverGutter) {
      node.style.zIndex = 5;
      node.style.position = "relative";
      if (!widget.noHScroll) node.style.marginLeft = -dims.gutterTotalWidth + "px";
    }
  }
  
  function updateSelection(cm) {