Handle Proxies

CHANGELOG.md

@@ -1,3 +1,7 @@
+# 1.1.0
+
+- Handle `Proxy`s
+
 # 1.0.0
 
 Initial release

README.md

@@ -11,6 +11,8 @@ iframes or Node.js [`vm`](https://nodejs.org/api/vm.html).
 
 # Example
 
+<!-- eslint-disable fp/no-proxy -->
+
 ```js
 import isErrorInstance from 'is-error-instance'
 
@@ -25,6 +27,17 @@ console.log(isErrorInstance(new AnyOtherError(''))) // true
 
 console.log(isErrorInstance(new DOMException(''))) // true
 console.log(isErrorInstance(new DOMError(''))) // true
+
+console.log(isErrorInstance(new Proxy(new Error(''), {}))) // true
+console.log(
+  isErrorInstance(
+    new Proxy(new Error(''), {
+      getPrototypeOf() {
+        throw new Error('')
+      },
+    }),
+  ),
+) // false
 ```
 
 # Install

src/main.js

@@ -1,6 +1,22 @@
 // Check if a value is an error instance
 export default function isErrorInstance(value) {
-  return value instanceof Error || ERROR_TAGS.has(protoToString.call(value))
+  return isInstanceOfError(value) || hasErrorTag(value)
+}
+
+const isInstanceOfError = function (value) {
+  try {
+    return value instanceof Error
+  } catch {
+    return false
+  }
+}
+
+const hasErrorTag = function (value) {
+  try {
+    return ERROR_TAGS.has(protoToString.call(value))
+  } catch {
+    return false
+  }
 }
 
 const ERROR_TAGS = new Set([

test/main.js

@@ -4,6 +4,15 @@ import test from 'ava'
 import isErrorInstance from 'is-error-instance'
 import { each } from 'test-each'
 
+each(
+  ['test', undefined, null, {}, Object.create(null)],
+  ({ title }, nonError) => {
+    test(`Detects non-errors | ${title}`, (t) => {
+      t.false(isErrorInstance(nonError))
+    })
+  },
+)
+
 // eslint-disable-next-line fp/no-class
 class ChildError extends Error {}
 // eslint-disable-next-line fp/no-mutation
@@ -27,10 +36,39 @@ each(
 )
 
 each(
-  ['test', undefined, null, {}, Object.create(null)],
-  ({ title }, nonError) => {
-    test(`Detects non-errors | ${title}`, (t) => {
-      t.false(isErrorInstance(nonError))
+  [
+    {
+      title: 'none',
+      proxy: {},
+      isError: true,
+    },
+    {
+      title: 'getPrototypeOf',
+      proxy: {
+        getPrototypeOf() {
+          throw new Error('unsafe')
+        },
+      },
+      isError: false,
+    },
+    {
+      title: 'get',
+      proxy: {
+        getPrototypeOf() {
+          throw new Error('unsafe')
+        },
+        get() {
+          throw new Error('unsafe')
+        },
+      },
+      isError: false,
+    },
+  ],
+  ({ title }, { proxy, isError }) => {
+    test(`Detects errors in proxy | ${title}`, (t) => {
+      // eslint-disable-next-line fp/no-proxy
+      const error = new Proxy(new Error('test'), proxy)
+      t.is(isErrorInstance(error), isError)
     })
   },
 )