[Fix] use a robust check for a boxed bigint

Author: ljharb

index.js

@@ -226,7 +226,17 @@ function isNumber(obj) { return toStr(obj) === '[object Number]' && (!hasToStrin
 function isBoolean(obj) { return toStr(obj) === '[object Boolean]' && (!hasToStringTag || !(Symbol.toStringTag in obj)); }
 // Symbol and BigInt do have Symbol.toStringTag by spec, so that can't be used to eliminate false positives
 function isSymbol(obj) { return toStr(obj) === '[object Symbol]'; }
-function isBigInt(obj) { return toStr(obj) === '[object BigInt]'; }
+
+function isBigInt(obj) {
+    if (!obj || typeof obj !== 'object' || !bigIntValueOf) {
+        return false;
+    }
+    try {
+        bigIntValueOf.call(obj);
+        return true;
+    } catch (e) {}
+    return false;
+}
 
 var hasOwn = Object.prototype.hasOwnProperty || function (key) { return key in this; };
 function has(obj, key) {

test/bigint.js

@@ -1,5 +1,8 @@
+'use strict';
+
 var inspect = require('../');
 var test = require('tape');
+var hasSymbols = require('has-symbols')();
 
 test('bigint', { skip: typeof BigInt === 'undefined' }, function (t) {
     t.test('primitives', function (st) {
@@ -27,5 +30,17 @@ test('bigint', { skip: typeof BigInt === 'undefined' }, function (t) {
         st.equal(inspect(Function('return 256n')()), '256n');
     });
 
+    t.test('toStringTag', { skip: !hasSymbols || typeof Symbol.toStringTag !== 'symbol' }, function (st) {
+        st.plan(1);
+
+        var faker = {};
+        faker[Symbol.toStringTag] = 'BigInt';
+        st.equal(
+            inspect(faker),
+            '{ [Symbol(Symbol.toStringTag)]: \'BigInt\' }',
+            'object lying about being a BigInt inspects as an object'
+        );
+    });
+
     t.end();
 });