fix: state leak when component is unmounted

When the component was unmounted before Google Optimize
was loaded, we had a state update that was causing an exception
on dev mode

Check if the component is unmounted before updating the state
fixes the issue

Author: ardeois

src/Experiment.js

@@ -3,6 +3,7 @@ import PropTypes from "prop-types";
 import OptimizeContext from "./OptimizeContext";
 
 class Experiment extends React.Component {
+  isUnmounted = false;
   state = {
     variant: null,
   };
@@ -48,7 +49,9 @@ class Experiment extends React.Component {
     );
     const oldHideEnd = window.dataLayer.hide.end;
     window.dataLayer.hide.end = () => {
-      this.updateVariantFromGlobalState();
+      if (!this.isUnmounted) {
+        this.updateVariantFromGlobalState();
+      }
       oldHideEnd && oldHideEnd();
     };
 
@@ -82,6 +85,7 @@ class Experiment extends React.Component {
 
   componentWillUnmount() {
     clearTimeout(this.updateVariantTimeout);
+    this.isUnmounted = true;
     typeof window !== "undefined" &&
       window.gtag &&
       window.gtag("event", "optimize.callback", {

test/specs/experiment.spec.js

@@ -4,6 +4,11 @@ import sinon from "sinon";
 import { Experiment } from "../../src";
 
 describe("experiment", () => {
+  afterEach(() => {
+    delete window.google_optimize;
+    delete window.dataLayer;
+  });
+
   it("should require experiment id", () => {
     expect(() => shallow(<Experiment />)).to.throw();
   });
@@ -50,5 +55,32 @@ describe("experiment", () => {
 
       expect(wrapper.find(Loader)).to.have.lengthOf(1);
     });
+
+    it("should update variant after optimize is loaded", () => {
+      delete window.dataLayer;
+      const wrapper = shallow(<Experiment id="abc" />);
+
+      expect(wrapper.state("variant")).to.be.equal(null);
+
+      // Load google optimize
+      window.google_optimize = { get: sinon.stub().returns("2") };
+      window.dataLayer.hide.end();
+
+      expect(wrapper.state("variant")).to.be.equal("2");
+    });
+
+    it("should not update variant after optimize is loaded if component was unmounted", () => {
+      delete window.dataLayer;
+      const wrapper = shallow(<Experiment id="abc" />);
+
+      expect(wrapper.state("variant")).to.be.equal(null);
+
+      wrapper.unmount();
+      // Load google optimize
+      window.google_optimize = { get: sinon.stub().returns("2") };
+
+      // If component state is updated while component is unmounted, this call will crash
+      window.dataLayer.hide.end();
+    });
   });
 });