[Fix] Map/Set: work around core-js bug < v2.5.0

Fixes #9

index.js

@@ -41,7 +41,7 @@ module.exports = function inspect_ (obj, opts, depth, seen) {
     else if (indexOf(seen, obj) >= 0) {
         return '[Circular]';
     }
-    
+
     function inspect (value, from) {
         if (from) {
             seen = seen.slice();
@@ -154,7 +154,12 @@ function isMap (x) {
     }
     try {
         mapSize.call(x);
-        return true;
+        try {
+            setSize.call(x);
+        } catch (s) {
+            return true;
+        }
+        return x instanceof Map; // core-js workaround, pre-v2.5.0
     } catch (e) {}
     return false;
 }
@@ -165,7 +170,12 @@ function isSet (x) {
     }
     try {
         setSize.call(x);
-        return true;
+        try {
+            mapSize.call(x);
+        } catch (m) {
+            return true;
+        }
+        return x instanceof Set; // core-js workaround, pre-v2.5.0
     } catch (e) {}
     return false;
 }

package.json

@@ -4,10 +4,12 @@
   "description": "string representations of objects in node and the browser",
   "main": "index.js",
   "devDependencies": {
+    "core-js": "^2.4.1",
     "tape": "^4.7.0"
   },
   "scripts": {
     "test": "npm run tests-only",
+    "pretests-only": "node test-core-js",
     "tests-only": "tape test/*.js"
   },
   "testling": {

test-core-js.js

@@ -0,0 +1,16 @@
+'use strict';
+
+require('core-js');
+
+var inspect = require('./');
+var test = require('tape');
+
+test('Maps', function (t) {
+    t.equal(inspect(new Map([[1, 2]])), 'Map (1) {1 => 2}');
+    t.end();
+});
+
+test('Sets', function (t) {
+    t.equal(inspect(new Set([[1, 2]])), 'Set (1) {[ 1, 2 ]}');
+    t.end();
+});