[New] add WeakRef support

Author: ljharb

.eslintrc

@@ -8,7 +8,7 @@
         "max-lines": 1,
         "max-lines-per-function": 1,
         "max-params": [2, 4],
-        "max-statements": [2, 100],
+        "max-statements": 0,
         "max-statements-per-line": [2, { "max": 2 }],
         "no-magic-numbers": 0,
         "no-param-reassign": 1,

index.js

@@ -10,6 +10,8 @@ var hasWeakMap = typeof WeakMap === 'function' && WeakMap.prototype;
 var weakMapHas = hasWeakMap ? WeakMap.prototype.has : null;
 var hasWeakSet = typeof WeakSet === 'function' && WeakSet.prototype;
 var weakSetHas = hasWeakSet ? WeakSet.prototype.has : null;
+var hasWeakRef = typeof WeakRef === 'function' && WeakRef.prototype;
+var weakRefDeref = hasWeakRef ? WeakRef.prototype.deref : null;
 var booleanValueOf = Boolean.prototype.valueOf;
 var objectToString = Object.prototype.toString;
 var functionToString = Function.prototype.toString;
@@ -173,6 +175,9 @@ module.exports = function inspect_(obj, options, depth, seen) {
     if (isWeakSet(obj)) {
         return weakCollectionOf('WeakSet');
     }
+    if (isWeakRef(obj)) {
+        return weakCollectionOf('WeakRef');
+    }
     if (isNumber(obj)) {
         return markBoxed(inspect(Number(obj)));
     }
@@ -279,6 +284,17 @@ function isWeakMap(x) {
     return false;
 }
 
+function isWeakRef(x) {
+    if (!weakRefDeref || !x || typeof x !== 'object') {
+        return false;
+    }
+    try {
+        weakRefDeref.call(x);
+        return true;
+    } catch (e) {}
+    return false;
+}
+
 function isSet(x) {
     if (!setSize || !x || typeof x !== 'object') {
         return false;

test/values.js

@@ -123,6 +123,22 @@ test('WeakSet', { skip: typeof WeakSet !== 'function' }, function (t) {
     t.end();
 });
 
+test('WeakRef', { skip: typeof WeakRef !== 'function' }, function (t) {
+    var ref = new WeakRef({ a: 1 });
+    var expectedString = 'WeakRef { ? }';
+    t.equal(inspect(ref), expectedString, 'new WeakRef({ a: 1 }) should not show contents');
+
+    t.end();
+});
+
+test('FinalizationRegistry', { skip: typeof FinalizationRegistry !== 'function' }, function (t) {
+    var registry = new FinalizationRegistry(function () {});
+    var expectedString = 'FinalizationRegistry [FinalizationRegistry] {}';
+    t.equal(inspect(registry), expectedString, 'new FinalizationRegistry(function () {}) should work normallys');
+
+    t.end();
+});
+
 test('Strings', function (t) {
     var str = 'abc';