diff --git a/src/codemirror/fcTemplateLang/index.js b/src/codemirror/fcTemplateLang/index.js
index f79b6741..f9af37ed 100644
--- a/src/codemirror/fcTemplateLang/index.js
+++ b/src/codemirror/fcTemplateLang/index.js
@@ -9,7 +9,7 @@ import {
 import { styleTags, tags as t } from '@lezer/highlight'
 import { parseMixed } from '@lezer/common'
 import { javascriptLanguage } from '@codemirror/lang-javascript'
-import { javascriptCompletionSources } from '../javascriptLang'
+import { javascriptCompletionSupport } from '../javascriptLang'
 import {
   xmlLanguage,
   completeFromSchema,
@@ -105,8 +105,6 @@ export function fcTemplateLang(options = {}) {
       )
     }),
     autoCloseTags,
-    javascriptLanguage.data.of({
-      autocomplete: javascriptCompletionSources(jsScope)
-    })
+    ...javascriptCompletionSupport(jsScope)
   ])
 }
diff --git a/src/codemirror/javascriptLang/index.js b/src/codemirror/javascriptLang/index.js
index 89980e57..c7722a19 100644
--- a/src/codemirror/javascriptLang/index.js
+++ b/src/codemirror/javascriptLang/index.js
@@ -1,10 +1,7 @@
-import { completeFromList } from '@codemirror/autocomplete'
 import {
   javascript,
   javascriptLanguage,
-  localCompletionSource,
-  scopeCompletionSource,
-  snippets
+  scopeCompletionSource
 } from '@codemirror/lang-javascript'
 import { nodeJsScope } from './nodeScope.js'
 
@@ -31,14 +28,20 @@ export function nodeScopeCompletionSource(autoCompleteObject) {
 }
 
 /**
- * Completions for mixed languages that mount `javascriptLanguage`
- * without `javascript()` (snippets + locals + Node globals).
+ * Support extensions for mixed languages that mount
+ * `javascriptLanguage` without `javascript()` itself (snippets,
+ * keywords, locals, and Node globals).
+ *
+ * Each source must be a separate `languageData` entry. CodeMirror
+ * treats an `autocomplete` *array* as `completeFromList` options, not
+ * as multiple completion sources.
  */
-export function javascriptCompletionSources(autoCompleteObject) {
+export function javascriptCompletionSupport(autoCompleteObject) {
   return [
-    completeFromList(snippets),
-    localCompletionSource,
-    nodeScopeCompletionSource(autoCompleteObject)
+    javascript().support,
+    javascriptLanguage.data.of({
+      autocomplete: nodeScopeCompletionSource(autoCompleteObject)
+    })
   ]
 }