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.

var step = Math.ceil(dist / 2), middle = from + step;
      if (bidi) {
        middle = from;
        for (var i = 0; i < step; ++i) middle = moveVisually(lineObj, middle, 1);
      }
      var middleX = getX(middle);
      if (middleX > x) {to = middle; toX = middleX; if (toOutside = wrongLine) toX += 1000; dist = step;}
      else {from = middle; fromX = middleX; fromOutside = wrongLine; dist -= step;}
    }
  }
  var measureText;
  function textHeight(display) {
    if (display.cachedTextHeight != null) return display.cachedTextHeight;
    if (measureText == null) {
      measureText = elt("pre");
      
      
      for (var i = 0; i < 49; ++i) {
        measureText.appendChild(document.createTextNode("x"));
        measureText.appendChild(elt("br"));
      }
      measureText.appendChild(document.createTextNode("x"));
    }
    removeChildrenAndAdd(display.measure, measureText);
    var height = measureText.offsetHeight / 50;
    if (height > 3) display.cachedTextHeight = height;
    removeChildren(display.measure);
    return height || 1;
  }
  function charWidth(display) {