diff --git a/Userland/Libraries/LibJS/Runtime/WeakSetPrototype.cpp b/Userland/Libraries/LibJS/Runtime/WeakSetPrototype.cpp
index 8058621a4d..46bcde5f95 100644
--- a/Userland/Libraries/LibJS/Runtime/WeakSetPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/WeakSetPrototype.cpp
@@ -18,6 +18,11 @@ void WeakSetPrototype::initialize(GlobalObject& global_object)
 {
     auto& vm = this->vm();
     Object::initialize(global_object);
+    u8 attr = Attribute::Writable | Attribute::Configurable;
+
+    define_native_function(vm.names.add, add, 1, attr);
+    define_native_function(vm.names.delete_, delete_, 1, attr);
+    define_native_function(vm.names.has, has, 1, attr);
 
     define_property(vm.well_known_symbol_to_string_tag(), js_string(global_object.heap(), vm.names.WeakSet), Attribute::Configurable);
 }
@@ -38,4 +43,41 @@ WeakSet* WeakSetPrototype::typed_this(VM& vm, GlobalObject& global_object)
     return static_cast<WeakSet*>(this_object);
 }
 
+JS_DEFINE_NATIVE_FUNCTION(WeakSetPrototype::add)
+{
+    auto* weak_set = typed_this(vm, global_object);
+    if (!weak_set)
+        return {};
+    auto value = vm.argument(0);
+    if (!value.is_object()) {
+        vm.throw_exception<TypeError>(global_object, ErrorType::NotAnObject, value.to_string_without_side_effects());
+        return {};
+    }
+    weak_set->values().set(&value.as_object(), AK::HashSetExistingEntryBehavior::Keep);
+    return weak_set;
+}
+
+JS_DEFINE_NATIVE_FUNCTION(WeakSetPrototype::delete_)
+{
+    auto* weak_set = typed_this(vm, global_object);
+    if (!weak_set)
+        return {};
+    auto value = vm.argument(0);
+    if (!value.is_object())
+        return Value(false);
+    return Value(weak_set->values().remove(&value.as_object()));
+}
+
+JS_DEFINE_NATIVE_FUNCTION(WeakSetPrototype::has)
+{
+    auto* weak_set = typed_this(vm, global_object);
+    if (!weak_set)
+        return {};
+    auto value = vm.argument(0);
+    if (!value.is_object())
+        return Value(false);
+    auto& values = weak_set->values();
+    return Value(values.find(&value.as_object()) != values.end());
+}
+
 }
diff --git a/Userland/Libraries/LibJS/Runtime/WeakSetPrototype.h b/Userland/Libraries/LibJS/Runtime/WeakSetPrototype.h
index 31a6a2cf96..5aee2fb630 100644
--- a/Userland/Libraries/LibJS/Runtime/WeakSetPrototype.h
+++ b/Userland/Libraries/LibJS/Runtime/WeakSetPrototype.h
@@ -20,4 +20,10 @@ public:
 
 private:
     static WeakSet* typed_this(VM&, GlobalObject&);
+
+    JS_DECLARE_NATIVE_FUNCTION(add);
+    JS_DECLARE_NATIVE_FUNCTION(delete_);
+    JS_DECLARE_NATIVE_FUNCTION(has);
+};
+
 }
diff --git a/Userland/Libraries/LibJS/Tests/builtins/WeakSet/WeakSet.prototype.add.js b/Userland/Libraries/LibJS/Tests/builtins/WeakSet/WeakSet.prototype.add.js
new file mode 100644
index 0000000000..0f77e94fe6
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/WeakSet/WeakSet.prototype.add.js
@@ -0,0 +1,16 @@
+test("basic functionality", () => {
+    expect(WeakSet.prototype.add).toHaveLength(1);
+
+    const weakSet = new WeakSet([{ a: 1 }, { a: 2 }, { a: 3 }]);
+    expect(weakSet.add({ a: 4 })).toBe(weakSet);
+    expect(weakSet.add({ a: 1 })).toBe(weakSet);
+});
+
+test("invalid values", () => {
+    const weakSet = new WeakSet();
+    [-100, Infinity, NaN, "hello", 152n].forEach(value => {
+        expect(() => {
+            weakSet.add(value);
+        }).toThrowWithMessage(TypeError, "is not an object");
+    });
+});
diff --git a/Userland/Libraries/LibJS/Tests/builtins/WeakSet/WeakSet.prototype.delete.js b/Userland/Libraries/LibJS/Tests/builtins/WeakSet/WeakSet.prototype.delete.js
new file mode 100644
index 0000000000..adfff46188
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/WeakSet/WeakSet.prototype.delete.js
@@ -0,0 +1,9 @@
+test("basic functionality", () => {
+    expect(WeakSet.prototype.delete).toHaveLength(1);
+
+    var original = [{ a: 1 }, { a: 2 }, { a: 3 }];
+    const weakSet = new WeakSet(original);
+    expect(weakSet.delete(original[0])).toBeTrue();
+    expect(weakSet.delete(original[0])).toBeFalse();
+    expect(weakSet.delete(null)).toBeFalse();
+});
diff --git a/Userland/Libraries/LibJS/Tests/builtins/WeakSet/WeakSet.prototype.has.js b/Userland/Libraries/LibJS/Tests/builtins/WeakSet/WeakSet.prototype.has.js
new file mode 100644
index 0000000000..3a8cfe021d
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/WeakSet/WeakSet.prototype.has.js
@@ -0,0 +1,12 @@
+test("length is 1", () => {
+    expect(WeakSet.prototype.has).toHaveLength(1);
+});
+
+test("basic functionality", () => {
+    var original = [{ a: 1 }, { a: 2 }, { a: 3 }];
+    var weakSet = new WeakSet(original);
+
+    expect(new WeakSet().has()).toBeFalse();
+    expect(weakSet.has(original[0])).toBeTrue();
+    expect(weakSet.has({ a: 1 })).toBeFalse();
+});