fix(core): Ensure fill only patches functions

Author: Lms24

packages/browser-utils/src/instrument/history.ts

@@ -64,10 +64,6 @@ export function instrumentHistory(): void {
     };
   }
 
-  if (typeof WINDOW.history.pushState === 'function') {
-    fill(WINDOW.history, 'pushState', historyReplacementFunction);
-  }
-  if (typeof WINDOW.history.replaceState === 'function') {
-    fill(WINDOW.history, 'replaceState', historyReplacementFunction);
-  }
+  fill(WINDOW.history, 'pushState', historyReplacementFunction);
+  fill(WINDOW.history, 'replaceState', historyReplacementFunction);
 }

packages/core/src/utils-hoist/object.ts

@@ -10,6 +10,8 @@ import { truncate } from './string';
 /**
  * Replace a method in an object with a wrapped version of itself.
  *
+ * If the method on the passed object is not a function, the wrapper will not be applied.
+ *
  * @param source An object that contains a method to be wrapped.
  * @param name The name of the method to be wrapped.
  * @param replacementFactory A higher-order function that takes the original version of the given method and returns a
@@ -23,7 +25,11 @@ export function fill(source: { [key: string]: any }, name: string, replacementFa
     return;
   }
 
-  const original = source[name] as () => any;
+  const original = source[name];
+  if (typeof original !== 'function') {
+    return;
+  }
+
   const wrapped = replacementFactory(original) as WrappedFunction;
 
   // Make sure it's a function first, as we need to attach an empty prototype for `defineProperties` to work

packages/core/test/utils-hoist/object.test.ts

@@ -54,6 +54,19 @@ describe('fill()', () => {
     expect(source.prop()).toEqual(41);
   });
 
+  test.each([42, null, undefined, {}])("does't throw if the property is not a function but %s", (propValue: any) => {
+    const source = {
+      foo: propValue,
+    };
+    const name = 'foo';
+    const replacement = vi.fn().mockImplementationOnce(cb => cb);
+
+    fill(source, name, replacement);
+
+    expect(source.foo).toEqual(propValue);
+    expect(replacement).not.toBeCalled();
+  });
+
   test('can do anything inside replacement function', () => {
     const source = {
       foo: (): number => 42,