Wrap JS functions with parenthesis before eval on the JS side

Author: mwouts

docs/changelog.md

@@ -10,6 +10,7 @@ ITables ChangeLog
 **Changed**
 - The `warn_on_undocumented_option` option now defaults to `True` and only check the option names
 - We have added a new option `warn_on_unexpected_option_type` that defaults to `warn_on_undocumented_option` when `typeguard>=4.4.1` is installed (`False` otherwise)
+- Wrapping JS function definitions in parentheses prior to JS eval is now done on the JS side.
 
 **Fixed**
 - We have added type hints to `itable.options` even for the options that don't have a default value ([#224](https://github.com/mwouts/itables/issues/224))

packages/dt_for_itables/CHANGELOG.md

@@ -1,6 +1,7 @@
 # 2.3.2+dev
 
 - We have made sure that the ordering icons on empty headers do not reappear when ordering a column
+- Wrapping Javascript functions definitions within parentheses before evaluating is now done on the Javascript side.
 
 # 2.3.2 (2025-05-17)
 

packages/dt_for_itables/src/index.js

@@ -59,7 +59,17 @@ function evalNestedKeys(obj, keys, context) {
     }
     if (rest.length === 0) {
         try {
-            obj[first] = window.eval(obj[first]);
+            let code = obj[first];
+            if (typeof code !== 'string') {
+                throw new Error(`Expected a string to evaluate in context '${context}', but got ${typeof code}.`);
+            }
+            if (/^\s*function\s*\(/.test(code)) {
+                // If the code matches the regular expression for a function definition,
+                // we wrap it in parentheses to proceed with the evaluation.
+                code = `(${code})`;
+            }
+
+            obj[first] = window.eval(code);
         }
         catch (e) {
             console.error(`Error evaluating ${context}='${obj[first]}'": ${e.message}`);

src/itables/javascript.py

@@ -277,11 +277,6 @@ def get_keys_to_be_evaluated(data) -> list[list[Union[int, str]]]:
         data = dict(enumerate(data))
     if isinstance(data, dict):
         for key, value in data.items():
-            if isinstance(value, JavascriptFunction):
-                # eval can't evaluate a function,
-                # but it can evaluate an expression that contains a function
-                # e.g. eval('(function() {return 5;})') does returns the function
-                data[key] = f"({value})"
             if isinstance(value, (JavascriptCode, JavascriptFunction)):
                 keys_to_be_evaluated.append([key])
             else:

src/itables/typing.py

@@ -1,3 +1,4 @@
+import re
 import warnings
 from importlib.metadata import PackageNotFoundError, version
 from pathlib import Path
@@ -17,9 +18,9 @@ class JavascriptFunction(str):
     """
 
     def __init__(self, value):
-        assert value.lstrip().startswith(
-            "function"
-        ), "A Javascript function is expected to start with 'function'"
+        assert re.compile(r"^\s*function\s*\(").match(
+            value
+        ), "A Javascript function is expected to start with 'function('"
 
 
 class JavascriptCode(str):