diff --git a/packages/form-js-editor/src/features/properties-panel/entries/JSFunctionEntry.js b/packages/form-js-editor/src/features/properties-panel/entries/JSFunctionEntry.js
index ccd86fee3..e1f987060 100644
--- a/packages/form-js-editor/src/features/properties-panel/entries/JSFunctionEntry.js
+++ b/packages/form-js-editor/src/features/properties-panel/entries/JSFunctionEntry.js
@@ -1,4 +1,4 @@
-import { FeelEntry, isFeelEntryEdited, TextAreaEntry, isTextAreaEntryEdited } from '@bpmn-io/properties-panel';
+import { FeelEntry, isFeelEntryEdited, TextAreaEntry, isTextAreaEntryEdited, ToggleSwitchEntry, isToggleSwitchEntryEdited } from '@bpmn-io/properties-panel';
 import { get } from 'min-dash';
 
 import { useService, useVariables } from '../hooks';
@@ -12,7 +12,7 @@ export function JSFunctionEntry(props) {
   const entries = [
     {
       id: 'variable-mappings',
-      component: VariableMappings,
+      component: FunctionParameters,
       editField: editField,
       field: field,
       isEdited: isFeelEntryEdited,
@@ -25,13 +25,21 @@ export function JSFunctionEntry(props) {
       field: field,
       isEdited: isTextAreaEntryEdited,
       isDefaultVisible: (field) => field.type === 'jsfunc'
+    },
+    {
+      id: 'on-load-only',
+      component: OnLoadOnlyEntry,
+      editField: editField,
+      field: field,
+      isEdited: isToggleSwitchEntryEdited,
+      isDefaultVisible: (field) => field.type === 'jsfunc'
     }
   ];
 
   return entries;
 }
 
-function VariableMappings(props) {
+function FunctionParameters(props) {
   const {
     editField,
     field,
@@ -42,7 +50,7 @@ function VariableMappings(props) {
 
   const variables = useVariables().map(name => ({ name }));
 
-  const path = [ 'variableMappings' ];
+  const path = [ 'functionParameters' ];
 
   const getValue = () => {
     return get(field, path, '');
@@ -52,13 +60,23 @@ function VariableMappings(props) {
     return editField(field, path, value || '');
   };
 
+  const tooltip = <div>
+    Functions parameters should be described as an object, e.g.:
+    <pre><code>{`{
+      name: user.name,
+      age: user.age
+    }`}</code></pre>
+  </div>;
+
   return FeelEntry({
     debounce,
     feel: 'required',
     element: field,
     getValue,
     id,
-    label: 'Variable mappings',
+    label: 'Function parameters',
+    tooltip,
+    description: 'Define the parameters to pass to the javascript context.',
     setValue,
     variables
   });
@@ -87,8 +105,35 @@ function FunctionDefinition(props) {
     debounce,
     element: field,
     getValue,
+    description: 'Access function parameters via `data`, set results with `setValue`, and register cleanup functions with `onCleanup`.',
+    id,
+    label: 'Javascript code',
+    setValue
+  });
+}
+
+function OnLoadOnlyEntry(props) {
+  const {
+    editField,
+    field,
+    id
+  } = props;
+
+  const path = [ 'onLoadOnly' ];
+
+  const getValue = () => {
+    return !!get(field, path, false);
+  };
+
+  const setValue = (value) => {
+    editField(field, path, value);
+  };
+
+  return ToggleSwitchEntry({
+    element: field,
     id,
-    label: 'Function',
+    label: 'Execute on load only',
+    getValue,
     setValue
   });
 }
diff --git a/packages/form-js-viewer/src/render/components/form-fields/JSFunctionField.js b/packages/form-js-viewer/src/render/components/form-fields/JSFunctionField.js
index 651249273..ec31603b8 100644
--- a/packages/form-js-viewer/src/render/components/form-fields/JSFunctionField.js
+++ b/packages/form-js-viewer/src/render/components/form-fields/JSFunctionField.js
@@ -1,26 +1,27 @@
-import { useCallback, useEffect } from 'preact/hooks';
-import { useExpressionEvaluation, useDeepCompareMemoize } from '../../hooks';
+import { useCallback, useEffect, useState } from 'preact/hooks';
+import { useExpressionEvaluation, useDeepCompareMemoize, usePrevious } from '../../hooks';
 import { isObject } from 'min-dash';
 
 const type = 'jsfunc';
 
 export function JSFunctionField(props) {
   const { field, onChange } = props;
-  const { jsFunction, variableMappings } = field;
+  const { jsFunction, functionParameters, onLoadOnly } = field;
 
-  const data = useExpressionEvaluation(variableMappings);
-  const dataMemo = useDeepCompareMemoize(data);
+  const [ loadLatch, setLoadLatch ] = useState(false);
 
-  const evaluateExpression = useCallback(() => {
-    try {
+  const paramsEval = useExpressionEvaluation(functionParameters);
+  const params = useDeepCompareMemoize(isObject(paramsEval) ? paramsEval : {});
 
-      // return early if no dependency data
-      if (!isObject(dataMemo) || !Object.keys(dataMemo).length) {
-        return;
-      }
+  const functionMemo = useCallback((params) => {
+
+    const cleanupCallbacks = [];
 
-      const func = new Function('data', 'setResult', jsFunction);
-      func(dataMemo, value => onChange({ field, value }));
+    try {
+
+      setLoadLatch(true);
+      const func = new Function('data', 'setValue', 'onCleanup', jsFunction);
+      func(params, value => onChange({ field, value }), callback => cleanupCallbacks.push(callback));
 
     } catch (error) {
 
@@ -32,11 +33,34 @@ export function JSFunctionField(props) {
       console.error('Error evaluating expression:', error);
       onChange({ field, value: null });
     }
-  }, [ jsFunction, dataMemo, field, onChange ]);
+
+    return () => {
+      cleanupCallbacks.forEach(fn => fn());
+    };
+
+  }, [ jsFunction, field, onChange ]);
+
+  const previousFunctionMemo = usePrevious(functionMemo);
+  const previousParams = usePrevious(params);
 
   useEffect(() => {
-    evaluateExpression();
-  }, [ evaluateExpression ]);
+
+    // reset load latch
+    if (!onLoadOnly && loadLatch) {
+      setLoadLatch(false);
+    }
+
+    const functionChanged = previousFunctionMemo !== functionMemo;
+    const paramsChanged = previousParams !== params;
+    const alreadyLoaded = onLoadOnly && loadLatch;
+
+    const shouldExecute = functionChanged || paramsChanged && !alreadyLoaded;
+
+    if (shouldExecute) {
+      return functionMemo(params);
+    }
+
+  }, [ previousFunctionMemo, functionMemo, previousParams, params, loadLatch, onLoadOnly ]);
 
   return null;
 }
@@ -48,6 +72,8 @@ JSFunctionField.config = {
   keyed: true,
   escapeGridRender: true,
   create: (options = {}) => ({
+    jsFunction: 'setValue(data.value)',
+    functionParameters: '={\n  value: 42\n}',
     ...options,
   })
 };