[New] ensure an Error’s cause is displayed

Author: ljharb

index.js

@@ -186,6 +186,9 @@ module.exports = function inspect_(obj, options, depth, seen) {
     }
     if (isError(obj)) {
         var parts = arrObjKeys(obj, inspect);
+        if ('cause' in obj && !isEnumerable.call(obj, 'cause')) {
+            return '{ [' + String(obj) + '] ' + $join.call($concat.call('[cause]: ' + inspect(obj.cause), parts), ', ') + ' }';
+        }
         if (parts.length === 0) { return '[' + String(obj) + ']'; }
         return '{ [' + String(obj) + '] ' + $join.call(parts, ', ') + ' }';
     }

package.json

@@ -9,6 +9,7 @@
     "aud": "^1.1.5",
     "auto-changelog": "^2.3.0",
     "core-js": "^2.6.12",
+    "error-cause": "^1.0.3",
     "es-value-fixtures": "^1.2.1",
     "eslint": "^8.5.0",
     "for-each": "^0.3.3",

test/err.js

@@ -1,5 +1,7 @@
-var inspect = require('../');
 var test = require('tape');
+var ErrorWithCause = require('error-cause/Error');
+
+var inspect = require('../');
 
 test('type error', function (t) {
     t.plan(1);
@@ -14,18 +16,33 @@ test('type error', function (t) {
     cerr.message = 'whoa';
     cerr['a-b'] = 5;
 
+    var withCause = new ErrorWithCause('foo', { cause: 'bar' });
+    var withCausePlus = new ErrorWithCause('foo', { cause: 'bar' });
+    withCausePlus.foo = 'bar';
+    var withUndefinedCause = new ErrorWithCause('foo', { cause: undefined });
+    var withEnumerableCause = new Error('foo');
+    withEnumerableCause.cause = 'bar';
+
     var obj = [
         new TypeError(),
         new TypeError('xxx'),
         aerr,
         berr,
-        cerr
+        cerr,
+        withCause,
+        withCausePlus,
+        withUndefinedCause,
+        withEnumerableCause
     ];
     t.equal(inspect(obj), '[ ' + [
         '[TypeError]',
         '[TypeError: xxx]',
         '{ [TypeError] foo: 555, bar: [ 1, 2, 3 ] }',
         '{ [TypeError: tuv] baz: 555 }',
-        '{ [SyntaxError: whoa] message: \'whoa\', \'a-b\': 5 }'
+        '{ [SyntaxError: whoa] message: \'whoa\', \'a-b\': 5 }',
+        '{ [Error: foo] [cause]: \'bar\' }',
+        '{ [Error: foo] [cause]: \'bar\', foo: \'bar\' }',
+        '{ [Error: foo] [cause]: undefined }',
+        '{ [Error: foo] cause: \'bar\' }'
     ].join(', ') + ' ]');
 });