assert: DRY .throws code

This refactors some code for less duplication.

Backport-PR-URL: #31431
PR-URL: #28263
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/assert.js

@@ -25,6 +25,7 @@ const {
   ObjectAssign,
   ObjectIs,
   ObjectKeys,
+  ObjectPrototypeIsPrototypeOf,
   Map,
 } = primordials;
 
@@ -571,6 +572,9 @@ function compareExceptionKey(actual, expected, key, message, keys, fn) {
 }
 
 function expectedException(actual, expected, message, fn) {
+  let generatedMessage = false;
+  let throwError = false;
+
   if (typeof expected !== 'function') {
     // Handle regular expressions.
     if (isRegExp(expected)) {
@@ -583,20 +587,9 @@ function expectedException(actual, expected, message, fn) {
         message = 'The input did not match the regular expression ' +
                   `${inspect(expected)}. Input:\n\n${inspect(str)}\n`;
       }
-
-      const err = new AssertionError({
-        actual,
-        expected,
-        message,
-        operator: fn.name,
-        stackStartFn: fn
-      });
-      err.generatedMessage = generatedMessage;
-      throw err;
-    }
-
-    // Handle primitives properly.
-    if (typeof actual !== 'object' || actual === null) {
+      throwError = true;
+      // Handle primitives properly.
+    } else if (typeof actual !== 'object' || actual === null) {
       const err = new AssertionError({
         actual,
         expected,
@@ -606,43 +599,52 @@ function expectedException(actual, expected, message, fn) {
       });
       err.operator = fn.name;
       throw err;
-    }
-
-    // Handle validation objects.
-    const keys = ObjectKeys(expected);
-    // Special handle errors to make sure the name and the message are compared
-    // as well.
-    if (expected instanceof Error) {
-      keys.push('name', 'message');
-    } else if (keys.length === 0) {
-      throw new ERR_INVALID_ARG_VALUE('error',
-                                      expected, 'may not be an empty object');
-    }
-    if (isDeepEqual === undefined) lazyLoadComparison();
-    for (const key of keys) {
-      if (typeof actual[key] === 'string' &&
-          isRegExp(expected[key]) &&
-          expected[key].test(actual[key])) {
-        continue;
+    } else {
+      // Handle validation objects.
+      const keys = ObjectKeys(expected);
+      // Special handle errors to make sure the name and the message are
+      // compared as well.
+      if (expected instanceof Error) {
+        keys.push('name', 'message');
+      } else if (keys.length === 0) {
+        throw new ERR_INVALID_ARG_VALUE('error',
+                                        expected, 'may not be an empty object');
+      }
+      if (isDeepEqual === undefined) lazyLoadComparison();
+      for (const key of keys) {
+        if (typeof actual[key] === 'string' &&
+            isRegExp(expected[key]) &&
+            expected[key].test(actual[key])) {
+          continue;
+        }
+        compareExceptionKey(actual, expected, key, message, keys, fn);
       }
-      compareExceptionKey(actual, expected, key, message, keys, fn);
+      return;
     }
-    return;
-  }
-
   // Guard instanceof against arrow functions as they don't have a prototype.
   // Check for matching Error classes.
-  if (expected.prototype !== undefined && actual instanceof expected) {
+  } else if (expected.prototype !== undefined && actual instanceof expected) {
     return;
-  }
-  if (Error.isPrototypeOf(expected)) {
+  } else if (ObjectPrototypeIsPrototypeOf(Error, expected)) {
     throw actual;
+  } else {
+    // Check validation functions return value.
+    const res = expected.call({}, actual);
+    if (res !== true) {
+      throw actual;
+    }
   }
 
-  // Check validation functions return value.
-  const res = expected.call({}, actual);
-  if (res !== true) {
-    throw actual;
+  if (throwError) {
+    const err = new AssertionError({
+      actual,
+      expected,
+      message,
+      operator: fn.name,
+      stackStartFn: fn
+    });
+    err.generatedMessage = generatedMessage;
+    throw err;
   }
 }