use ‘util.inspect.custom’ if available

index.js

@@ -37,23 +37,37 @@
 
   'use strict';
 
+  var util = {inspect: {}};
+
   /* istanbul ignore else */
   if (typeof module === 'object' && typeof module.exports === 'object') {
-    module.exports = f ();
+    module.exports = f (require ('util'));
   } else if (typeof define === 'function' && define.amd != null) {
-    define ([], f);
+    define ([], function() { return f (util); });
   } else {
-    self.sanctuaryUseless = f ();
+    self.sanctuaryUseless = f (util);
   }
 
-} (function() {
+} (function(util) {
 
   'use strict';
 
-  return {
-    constructor: {'@@type': 'sanctuary-useless/Useless@1'},
-    inspect: function() { return 'Useless'; }
-  };
+  var Useless = {};
+
+  Useless.constructor = {'@@type': 'sanctuary-useless/Useless@1'};
+
+  function inspect() {
+    return 'Useless';
+  }
+  var custom = util.inspect.custom;
+  /* istanbul ignore else */
+  if (typeof custom === 'symbol') {
+    Useless[custom] = inspect;
+  } else {
+    Useless.inspect = inspect;
+  }
+
+  return Useless;
 
 }));
 

test/index.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const assert        = require ('assert');
+const util          = require ('util');
 
 const show          = require ('sanctuary-show');
 const Z             = require ('sanctuary-type-classes');
@@ -26,7 +27,7 @@ test ('Useless', () => {
      ({namespace: 'sanctuary-useless', name: 'Useless', version: 1});
 
   eq (String (Useless)) ('[object Object]');
-  eq (Useless.inspect ()) ('Useless');
+  eq (util.inspect (Useless)) ('Useless');
 
   eq (Z.Setoid.test (Useless)) (false);
   eq (Z.Ord.test (Useless)) (false);