util: display constructor name when inspecting objects

lib/util.js

@@ -167,6 +167,22 @@ function arrayToHash(array) {
 }
 
 
+function getConstructorOf(obj) {
+  while (obj) {
+    var descriptor = Object.getOwnPropertyDescriptor(obj, 'constructor');
+    if (descriptor !== undefined &&
+        typeof descriptor.value === 'function' &&
+        descriptor.value.name !== '') {
+      return descriptor.value;
+    }
+
+    obj = Object.getPrototypeOf(obj);
+  }
+
+  return null;
+}
+
+
 function inspectPromise(p) {
   Debug = Debug || require('vm').runInDebugContext('Debug');
   var mirror = Debug.MakeMirror(p, true);
@@ -260,14 +276,17 @@ function formatValue(ctx, value, recurseTimes) {
     }
   }
 
+  var constructor = getConstructorOf(value);
   var base = '', empty = false, braces, formatter;
 
   if (Array.isArray(value)) {
+    if (constructor === Array)
+      constructor = null;
     braces = ['[', ']'];
     empty = value.length === 0;
     formatter = formatArray;
   } else if (value instanceof Set) {
-    braces = ['Set {', '}'];
+    braces = ['{', '}'];
     // With `showHidden`, `length` will display as a hidden property for
     // arrays. For consistency's sake, do the same for `size`, even though this
     // property isn't selected by Object.getOwnPropertyNames().
@@ -276,7 +295,7 @@ function formatValue(ctx, value, recurseTimes) {
     empty = value.size === 0;
     formatter = formatSet;
   } else if (value instanceof Map) {
-    braces = ['Map {', '}'];
+    braces = ['{', '}'];
     // Ditto.
     if (ctx.showHidden)
       keys.unshift('size');
@@ -286,9 +305,11 @@ function formatValue(ctx, value, recurseTimes) {
     // Only create a mirror if the object superficially looks like a Promise.
     var promiseInternals = value instanceof Promise && inspectPromise(value);
     if (promiseInternals) {
-      braces = ['Promise {', '}'];
+      braces = ['{', '}'];
       formatter = formatPromise;
     } else {
+      if (constructor === Object)
+        constructor = null;
       braces = ['{', '}'];
       empty = true;  // No other data than keys.
       formatter = formatObject;
@@ -336,6 +357,10 @@ function formatValue(ctx, value, recurseTimes) {
     base = ' ' + '[Boolean: ' + formatted + ']';
   }
 
+  // Add constructor name if available
+  if (base === '' && constructor)
+    braces[0] = constructor.name + ' ' + braces[0];
+
   if (empty === true) {
     return braces[0] + base + braces[1];
   }

test/parallel/test-sys.js

@@ -17,7 +17,7 @@ assert.equal(new Date('2010-02-14T12:48:40+01:00').toString(),
 assert.equal("'\\n\\u0001'", common.inspect('\n\u0001'));
 
 assert.equal('[]', common.inspect([]));
-assert.equal('{}', common.inspect(Object.create([])));
+assert.equal('Array {}', common.inspect(Object.create([])));
 assert.equal('[ 1, 2 ]', common.inspect([1, 2]));
 assert.equal('[ 1, [ 2, 3 ] ]', common.inspect([1, [2, 3]]));
 

test/parallel/test-util-inspect.js

@@ -61,7 +61,7 @@ assert.ok(ex.indexOf('[message]') != -1);
 
 // GH-1941
 // should not throw:
-assert.equal(util.inspect(Object.create(Date.prototype)), '{}');
+assert.equal(util.inspect(Object.create(Date.prototype)), 'Date {}');
 
 // GH-1944
 assert.doesNotThrow(function() {
@@ -306,3 +306,44 @@ checkAlignment(function() {
 }());
 checkAlignment(new Set(big_array));
 checkAlignment(new Map(big_array.map(function(y) { return [y, null]; })));
+
+
+// Test display of constructors
+
+class ObjectSubclass {}
+class ArraySubclass extends Array {}
+class SetSubclass extends Set {}
+class MapSubclass extends Map {}
+class PromiseSubclass extends Promise {}
+
+var x = new ObjectSubclass();
+x.foo = 42;
+assert.equal(util.inspect(x),
+             'ObjectSubclass { foo: 42 }');
+assert.equal(util.inspect(new ArraySubclass(1, 2, 3)),
+             'ArraySubclass [ 1, 2, 3 ]');
+assert.equal(util.inspect(new SetSubclass([1, 2, 3])),
+             'SetSubclass { 1, 2, 3 }');
+assert.equal(util.inspect(new MapSubclass([['foo', 42]])),
+            'MapSubclass { \'foo\' => 42 }');
+assert.equal(util.inspect(new PromiseSubclass(function() {})),
+             'PromiseSubclass { <pending> }');
+
+// Corner cases.
+var x = { constructor: 42 };
+assert.equal(util.inspect(x), '{ constructor: 42 }');
+
+var x = {};
+Object.defineProperty(x, 'constructor', {
+  get: function() {
+    throw new Error('should not access constructor');
+  },
+  enumerable: true
+});
+assert.equal(util.inspect(x), '{ constructor: [Getter] }');
+
+var x = new (function() {});
+assert.equal(util.inspect(x), '{}');
+
+var x = Object.create(null);
+assert.equal(util.inspect(x), '{}');