diff --git a/.idea/is.iml b/.idea/is.iml
new file mode 100644
index 0000000..0c8867d
--- /dev/null
+++ b/.idea/is.iml
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="WEB_MODULE" version="4">
+  <component name="NewModuleRootManager">
+    <content url="file://$MODULE_DIR$">
+      <excludeFolder url="file://$MODULE_DIR$/temp" />
+      <excludeFolder url="file://$MODULE_DIR$/.tmp" />
+      <excludeFolder url="file://$MODULE_DIR$/tmp" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>
\ No newline at end of file
diff --git a/.idea/modules.xml b/.idea/modules.xml
new file mode 100644
index 0000000..5cdc77d
--- /dev/null
+++ b/.idea/modules.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/.idea/is.iml" filepath="$PROJECT_DIR$/.idea/is.iml" />
+    </modules>
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/vcs.xml b/.idea/vcs.xml
new file mode 100644
index 0000000..94a25f7
--- /dev/null
+++ b/.idea/vcs.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/workspace.xml b/.idea/workspace.xml
new file mode 100644
index 0000000..e5aeaf9
--- /dev/null
+++ b/.idea/workspace.xml
@@ -0,0 +1,87 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ChangeListManager">
+    <list default="true" id="df737647-19a6-4a5f-88a0-8ce9d29a36c8" name="Changes" comment="">
+      <change beforePath="$PROJECT_DIR$/package.json" beforeDir="false" afterPath="$PROJECT_DIR$/package.json" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/test/test.ts" beforeDir="false" afterPath="$PROJECT_DIR$/test/test.ts" afterDir="false" />
+    </list>
+    <option name="SHOW_DIALOG" value="false" />
+    <option name="HIGHLIGHT_CONFLICTS" value="true" />
+    <option name="HIGHLIGHT_NON_ACTIVE_CHANGELIST" value="false" />
+    <option name="LAST_RESOLUTION" value="IGNORE" />
+  </component>
+  <component name="Git.Settings">
+    <option name="RECENT_GIT_ROOT_PATH" value="$PROJECT_DIR$" />
+  </component>
+  <component name="MacroExpansionManager">
+    <option name="directoryName" value="hl7nkx35" />
+  </component>
+  <component name="MarkdownSettingsMigration">
+    <option name="stateVersion" value="1" />
+  </component>
+  <component name="ProjectId" id="25cK4TvoIxGKxbzN8247wytmhpC" />
+  <component name="ProjectViewState">
+    <option name="hideEmptyMiddlePackages" value="true" />
+    <option name="showLibraryContents" value="true" />
+  </component>
+  <component name="PropertiesComponent"><![CDATA[{
+  "keyToString": {
+    "WebServerToolWindowFactoryState": "false",
+    "last_opened_file_path": "/Users/wangbinlin/Project/daily_exercise/is",
+    "nodejs_package_manager_path": "npm",
+    "ts.external.directory.path": "/Users/wangbinlin/Project/daily_exercise/is/node_modules/typescript/lib",
+    "vue.rearranger.settings.migration": "true"
+  }
+}]]></component>
+  <component name="RunManager" selected="Node.js.index.js">
+    <configuration name="index.js" type="NodeJSConfigurationType" temporary="true" nameIsGenerated="true" path-to-js-file="$PROJECT_DIR$/source/index.js" working-dir="$PROJECT_DIR$/source">
+      <method v="2" />
+    </configuration>
+    <configuration name="test.js" type="NodeJSConfigurationType" temporary="true" nameIsGenerated="true" path-to-js-file="$PROJECT_DIR$/test/test.js" working-dir="$PROJECT_DIR$/test">
+      <method v="2" />
+    </configuration>
+    <recent_temporary>
+      <list>
+        <item itemvalue="Node.js.index.js" />
+        <item itemvalue="Node.js.test.js" />
+      </list>
+    </recent_temporary>
+  </component>
+  <component name="SpellCheckerSettings" RuntimeDictionaries="0" Folders="0" CustomDictionaries="0" DefaultDictionary="application-level" UseSingleDictionary="true" transferred="true" />
+  <component name="TaskManager">
+    <task active="true" id="Default" summary="Default task">
+      <changelist id="df737647-19a6-4a5f-88a0-8ce9d29a36c8" name="Changes" comment="" />
+      <created>1645820743983</created>
+      <option name="number" value="Default" />
+      <option name="presentableId" value="Default" />
+      <updated>1645820743983</updated>
+      <workItem from="1645820745885" duration="3571000" />
+      <workItem from="1645962952689" duration="7278000" />
+      <workItem from="1646150741729" duration="7294000" />
+      <workItem from="1646315541343" duration="840000" />
+      <workItem from="1646820573494" duration="13927000" />
+      <workItem from="1654745859867" duration="730000" />
+      <workItem from="1654783293999" duration="6422000" />
+    </task>
+    <servers />
+  </component>
+  <component name="TypeScriptGeneratedFilesManager">
+    <option name="version" value="3" />
+    <option name="exactExcludedFiles">
+      <list>
+        <option value="$PROJECT_DIR$/source/index.js" />
+      </list>
+    </option>
+  </component>
+  <component name="Vcs.Log.Tabs.Properties">
+    <option name="TAB_STATES">
+      <map>
+        <entry key="MAIN">
+          <value>
+            <State />
+          </value>
+        </entry>
+      </map>
+    </option>
+  </component>
+</project>
\ No newline at end of file
diff --git a/package.json b/package.json
index a1f4653..d07c4b4 100644
--- a/package.json
+++ b/package.json
@@ -53,7 +53,6 @@
 		"@types/zen-observable": "^0.8.0",
 		"@typescript-eslint/eslint-plugin": "^2.20.0",
 		"@typescript-eslint/parser": "^2.20.0",
-		"@ungap/weakrefs": "^0.2.0",
 		"ava": "^3.3.0",
 		"del-cli": "^2.0.0",
 		"eslint-config-xo-typescript": "^0.26.0",
diff --git a/test/test.ts b/test/test.ts
index f9b6091..2b6e170 100644
--- a/test/test.ts
+++ b/test/test.ts
@@ -7,7 +7,6 @@ import {JSDOM} from 'jsdom';
 import {Subject, Observable} from 'rxjs';
 import tempy = require('tempy');
 import ZenObservable = require('zen-observable');
-import {WeakRef} from '@ungap/weakrefs'
 import is, {assert, AssertionTypeDescription, Primitive, TypedArray, TypeName} from '../source';
 
 class PromiseSubclassFixture<T> extends Promise<T> {}
@@ -339,9 +338,7 @@ const types = new Map<string, Test>([
 	['weakRef', {
 		is: is.weakRef,
 		assert: assert.weakRef,
-		fixtures: [
-			window.WeakRef ? new window.WeakRef({}) : new WeakRef({})
-		],
+		fixtures: window.WeakRef ? [new window.WeakRef({})] : [],
 		typename: 'WeakRef'
 	}],
 	['weakMap', {