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 missed = false;
    cm.display.pollingFast = true;
    function p() {
      var changed = readInput(cm);
      if (!changed && !missed) {missed = true; cm.display.poll.set(60, p);}
      else {cm.display.pollingFast = false; slowPoll(cm);}
    }
    cm.display.poll.set(20, p);
  }
  
  
  
  
  
  function readInput(cm) {
    var input = cm.display.input, prevInput = cm.display.prevInput, doc = cm.doc, sel = doc.sel;
    if (!cm.state.focused || hasSelection(input) || isReadOnly(cm) || cm.state.disableInput) return false;
    if (cm.state.pasteIncoming && cm.state.fakedLastChar) {
      input.value = input.value.substring(0, input.value.length - 1);
      cm.state.fakedLastChar = false;
    }
    var text = input.value;
    if (text == prevInput && posEq(sel.from, sel.to)) return false;
    if (ie && !ie_lt9 && cm.display.inputHasSelection === text) {
      resetInput(cm, true);
      return false;
    }
    var withOp = !cm.curOp;
    if (withOp) startOperation(cm);
    sel.shift = false;