diff --git a/chainforge/react-server/src/App.js b/chainforge/react-server/src/App.js
index 949b74c..cabaaa5 100644
--- a/chainforge/react-server/src/App.js
+++ b/chainforge/react-server/src/App.js
@@ -106,9 +106,14 @@ const App = () => {
     const { x, y } = getViewportCenter();
     addNode({ id: 'promptNode-'+Date.now(), type: 'prompt', data: { prompt: '' }, position: {x: x-200, y:y-100} });
   };
-  const addEvalNode = (event) => {
+  const addEvalNode = (progLang) => {
     const { x, y } = getViewportCenter();
-    addNode({ id: 'evalNode-'+Date.now(), type: 'evaluator', data: { code: "def evaluate(response):\n  return len(response.text)" }, position: {x: x-200, y:y-100} });
+    let code = "";
+    if (progLang === 'python') 
+      code = "def evaluate(response):\n  return len(response.text)";
+    else if (progLang === 'javascript')
+      code = "function evaluate(resp) {\n  return resp.text.length;\n}";
+    addNode({ id: 'evalNode-'+Date.now(), type: 'evaluator', data: { language: progLang, code: code }, position: {x: x-200, y:y-100} });
   };
   const addVisNode = (event) => {
     const { x, y } = getViewportCenter();
@@ -465,7 +470,8 @@ const App = () => {
           <Menu.Dropdown>
               <Menu.Item onClick={addTextFieldsNode} icon={<IconTextPlus size="16px" />}> TextFields </Menu.Item>
               <Menu.Item onClick={addPromptNode} icon={'💬'}> Prompt Node </Menu.Item>
-              <Menu.Item onClick={addEvalNode} icon={<IconTerminal size="16px" />}> Evaluator Node </Menu.Item>
+              <Menu.Item onClick={() => addEvalNode('javascript')} icon={<IconTerminal size="16px" />}> JavaScript Evaluator Node </Menu.Item>
+              <Menu.Item onClick={() => addEvalNode('python')} icon={<IconTerminal size="16px" />}> Python Evaluator Node </Menu.Item>
               <Menu.Item onClick={addVisNode} icon={'📊'}> Vis Node </Menu.Item>
               <Menu.Item onClick={addInspectNode} icon={'🔍'}> Inspect Node </Menu.Item>
               <Menu.Item onClick={addCsvNode} icon={<IconCsv size="16px" />}> CSV Node </Menu.Item>
diff --git a/chainforge/react-server/src/EvaluatorNode.js b/chainforge/react-server/src/EvaluatorNode.js
index 43cac77..6d714db 100644
--- a/chainforge/react-server/src/EvaluatorNode.js
+++ b/chainforge/react-server/src/EvaluatorNode.js
@@ -9,6 +9,7 @@ import LLMResponseInspectorModal from './LLMResponseInspectorModal';
 // Ace code editor
 import AceEditor from "react-ace";
 import "ace-builds/src-noconflict/mode-python";
+import "ace-builds/src-noconflict/mode-javascript";
 import "ace-builds/src-noconflict/theme-xcode";
 import "ace-builds/src-noconflict/ext-language_tools";
 import fetch_from_backend from './fetch_from_backend';
@@ -28,8 +29,14 @@ const EvaluatorNode = ({ data, id }) => {
   // For a way to inspect responses without having to attach a dedicated node
   const inspectModal = useRef(null);
 
+  // The programming language for the editor. Also determines what 'execute'
+  // function will ultimately be called.
+  const [progLang, setProgLang] = useState(data.language || 'python');
+
+  // The text in the code editor. 
   const [codeText, setCodeText] = useState(data.code);
   const [codeTextOnLastRun, setCodeTextOnLastRun] = useState(false);
+
   const [lastRunLogs, setLastRunLogs] = useState("");
   const [lastResponses, setLastResponses] = useState([]);
   const [lastRunSuccess, setLastRunSuccess] = useState(true);
@@ -85,7 +92,8 @@ const EvaluatorNode = ({ data, id }) => {
     }
 
     // Double-check that the code includes an 'evaluate' function:
-    if (codeText.search(/def\s+evaluate\s*(.*):/) === -1) {
+    const find_evalfunc_regex = progLang === 'python' ? /def\s+evaluate\s*(.*):/ : /function\s+evaluate\s*(.*)/;
+    if (codeText.search(find_evalfunc_regex) === -1) {
       const err_msg = `Could not find required function 'evaluate'. Make sure you have defined an 'evaluate' function.`;
       setStatus('error');
       alertModal.current.trigger(err_msg);
@@ -107,11 +115,12 @@ const EvaluatorNode = ({ data, id }) => {
 
     // Run evaluator in backend
     const codeTextOnRun = codeText + '';
-    fetch_from_backend('execute', {
+    const execute_route = (progLang === 'python') ? 'execute' : 'executejs';
+    fetch_from_backend(execute_route, {
       id: id,
       code: codeTextOnRun,
-      scope: mapScope,
       responses: input_node_ids,
+      scope: mapScope,
       reduce_vars: [],
       script_paths: script_paths,
     }, rejected).then(function(json) {
@@ -163,7 +172,10 @@ const EvaluatorNode = ({ data, id }) => {
 
   return (
     <div className="evaluator-node cfnode">
-      <NodeLabel title={data.title || 'Python Evaluator Node'} 
+      <NodeLabel title={data.title || 
+                        progLang === 'python' ? 
+                          'Python Evaluator Node'
+                          : 'JavaScript Evaluator Node' } 
                   nodeId={id} 
                   onEdit={hideStatusIndicator}
                   icon={<IconTerminal size="16px" />} 
@@ -197,7 +209,7 @@ const EvaluatorNode = ({ data, id }) => {
         {/* <span className="code-style">response</span>: */}
         <div className="ace-editor-container nodrag">
           <AceEditor
-            mode="python"
+            mode={progLang}
             theme="xcode"
             onChange={handleCodeChange}
             value={data.code}
@@ -206,6 +218,7 @@ const EvaluatorNode = ({ data, id }) => {
             width='100%'
             height='100px'
             style={{minWidth:'310px'}}
+            setOptions={{useWorker: false}}
             tabSize={2}
             onLoad={editorInstance => {  // Make Ace Editor div resizeable. 
               editorInstance.container.style.resize = "both";
diff --git a/chainforge/react-server/src/backend/__test__/backend.test.ts b/chainforge/react-server/src/backend/__test__/backend.test.ts
index d1058bd..028fb29 100644
--- a/chainforge/react-server/src/backend/__test__/backend.test.ts
+++ b/chainforge/react-server/src/backend/__test__/backend.test.ts
@@ -3,7 +3,7 @@
 */
 import { LLM } from '../models';
 import { expect, test } from '@jest/globals';
-import { queryLLM, execute, ResponseInfo } from '../backend';
+import { queryLLM, executejs, ResponseInfo } from '../backend';
 import { StandardizedLLMResponse } from '../typing';
 import StorageCache from '../cache';
 
@@ -48,7 +48,7 @@ test('run evaluate func over responses', async () => {
 // `;
 
   // Execute the code, and map the evaluate function over all responses
-  const {responses, logs, error} = await execute('evalid', code, ['dummy_response_id'], 'response');
+  const {responses, logs, error} = await executejs('evalid', code, ['dummy_response_id'], 'response');
 
   // There should be no errors
   if (error)
diff --git a/chainforge/react-server/src/backend/backend.ts b/chainforge/react-server/src/backend/backend.ts
index 4dcd1c2..8a7ef2b 100644
--- a/chainforge/react-server/src/backend/backend.ts
+++ b/chainforge/react-server/src/backend/backend.ts
@@ -642,20 +642,22 @@ export async function queryLLM(id: string,
  * @param response_ids the cache'd response to run on, which must be a unique ID or list of unique IDs of cache'd data
  * @param scope the scope of responses to run on --a single response, or all across each batch. (If batch, evaluate() func has access to 'responses'.)
  */
-export async function execute(id: string, 
-                              code: string | ((rinfo: ResponseInfo) => any), 
-                              response_ids: string | string[], 
-                              scope: 'response' | 'batch'): Promise<Dict> {
+export async function executejs(id: string, 
+                                code: string | ((rinfo: ResponseInfo) => any), 
+                                response_ids: string | string[], 
+                                scope: 'response' | 'batch'): Promise<Dict> {
   // Check format of response_ids
   if (!Array.isArray(response_ids))
     response_ids = [ response_ids ];
   response_ids = response_ids as Array<string>;
 
+  console.log('executing js');
+
   // const iframe = document.createElement('iframe');
 
   // Instantiate the evaluator function by eval'ing the passed code
   // DANGER DANGER!!
-  let iframe: HTMLIFrameElement | undefined;
+  let iframe: HTMLElement | undefined;
   if (typeof code === 'string') {
     try {
         /*
@@ -667,7 +669,7 @@ export async function execute(id: string,
           The Evaluate node in the front-end has a hidden iframe with the following id. 
           We need to get this iframe element. 
         */
-        let iframe = document.getElementById(`${id}-iframe`);
+        iframe = document.getElementById(`${id}-iframe`);
         if (!iframe)
           throw new Error("Could not find iframe sandbox for evaluator node.");
 
diff --git a/chainforge/react-server/src/fetch_from_backend.js b/chainforge/react-server/src/fetch_from_backend.js
index 8d64f12..6a21303 100644
--- a/chainforge/react-server/src/fetch_from_backend.js
+++ b/chainforge/react-server/src/fetch_from_backend.js
@@ -1,5 +1,4 @@
-// import { queryLLM, execute } from "./backend/backend.ts";
-import { queryLLM, execute } from "./backend/backend";
+import { queryLLM, executejs } from "./backend/backend";
 
 const BACKEND_TYPES = {
   FLASK: 'flask',
@@ -15,7 +14,7 @@ async function _route_to_js_backend(route, params) {
     case 'queryllm':
       return queryLLM(...Object.values(params));
     case 'executejs':
-      return execute(...Object.values(params));
+      return executejs(params.id, params.code, params.responses, params.scope);
     default:
       throw new Error(`Could not find backend function for route named ${route}`);
   }
@@ -30,6 +29,11 @@ async function _route_to_js_backend(route, params) {
  */
 export default function fetch_from_backend(route, params, rejected) {
   rejected = rejected || ((err) => {throw new Error(err)});
+
+  if (route === 'executejs') {
+    return _route_to_js_backend(route, params);
+  }
+
   switch (BACKEND_TYPE) {
     case BACKEND_TYPES.FLASK:  // Fetch from Flask (python) backend
       return fetch(`${FLASK_BASE_URL}app/${route}`, {
@@ -49,4 +53,4 @@ export default function fetch_from_backend(route, params, rejected) {
 
 export function set_backend_type(t) {
   BACKEND_TYPE = t;
-}
\ No newline at end of file
+}