diff --git a/README.md b/README.md
index 14c421ab44..05d1560f0b 100644
--- a/README.md
+++ b/README.md
@@ -32,17 +32,13 @@ Please note that doing this will disable the test suite, so you will need to run
 cd scripts\
 bash test.sh
 
-## For Testing of js-slang
+## js-slang
 
-### Alpha version
-
-Use branch js-slang-alpha-preview to see the new changes (native and verbose errors).
-
-Have `"enable verbose";` as the first line of your program to activate verbose messages.
+Currently using a version of js-slang with native and verbose errors.
 
 Edit https://github.com/source-academy/cadet-frontend/blob/57ba44f6b55c214d0f20339cd45bece57f24f48c/src/sagas/index.ts#L260
 
-to toggle native.
+to toggle native (default is native enabled). 
 
 ### To run local copy of js-slang
 
diff --git a/package.json b/package.json
index 2b9c80ce70..42f50b1392 100644
--- a/package.json
+++ b/package.json
@@ -37,7 +37,7 @@
     "draft-js": "^0.10.5",
     "flexboxgrid": "^6.3.1",
     "flexboxgrid-helpers": "^1.1.3",
-    "js-slang": "0.2.0",
+    "js-slang": "0.2.1-alpha.4",
     "lodash": "^4.17.11",
     "lz-string": "^1.4.4",
     "moment": "^2.22.2",
diff --git a/src/mocks/context.ts b/src/mocks/context.ts
index f8047551bf..6ae96da29c 100644
--- a/src/mocks/context.ts
+++ b/src/mocks/context.ts
@@ -2,7 +2,7 @@ import { parse } from 'acorn';
 import { FunctionExpression } from 'estree';
 import Closure from 'js-slang/dist/closure';
 import createContext from 'js-slang/dist/createContext';
-import { Context, Frame } from 'js-slang/dist/types';
+import { Context, Environment } from 'js-slang/dist/types';
 import { TypeError } from 'js-slang/dist/utils/rttc';
 
 export function mockContext(chapter = 1): Context {
@@ -13,7 +13,7 @@ export function mockRuntimeContext(): Context {
   const context = createContext();
   context.runtime = {
     isRunning: true,
-    frames: [],
+    environments: [],
     nodes: [
       {
         type: 'Literal',
@@ -31,7 +31,7 @@ export function mockRuntimeContext(): Context {
 }
 
 export function mockClosure(): Closure {
-  return new Closure({} as FunctionExpression, {} as Frame, {} as Context);
+  return new Closure({} as FunctionExpression, {} as Environment, {} as Context);
 }
 
 export function mockTypeError(): TypeError {
diff --git a/src/sagas/index.ts b/src/sagas/index.ts
index 779321f5b1..d595479c89 100644
--- a/src/sagas/index.ts
+++ b/src/sagas/index.ts
@@ -257,7 +257,7 @@ function* playgroundSaga(): SagaIterator {
 
 function* evalCode(code: string, context: Context, location: WorkspaceLocation) {
   const { result, interrupted } = yield race({
-    result: call(runInContext, code, context, { scheduler: 'preemptive' }),
+    result: call(runInContext, code, context, { scheduler: 'preemptive', isNativeRunnable: true }),
     /**
      * A BEGIN_INTERRUPT_EXECUTION signals the beginning of an interruption,
      * i.e the trigger for the interpreter to interrupt execution.
diff --git a/yarn.lock b/yarn.lock
index 4d4a1315ec..77c25324cd 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -5227,9 +5227,10 @@ js-base64@^2.1.9:
   version "2.4.3"
   resolved "https://registry.yarnpkg.com/js-base64/-/js-base64-2.4.3.tgz#2e545ec2b0f2957f41356510205214e98fad6582"
 
-js-slang@0.2.0:
-  version "0.2.0"
-  resolved "https://registry.yarnpkg.com/js-slang/-/js-slang-0.2.0.tgz#15b998d2e67bc2834421235f96408b4015bb322c"
+js-slang@0.2.1-alpha.3:
+  version "0.2.1-alpha.3"
+  resolved "https://registry.yarnpkg.com/js-slang/-/js-slang-0.2.1-alpha.3.tgz#8e93828c67e0eb729ce229f66cadc5e081730541"
+  integrity sha512-iLEhlsrW1kbZ1OZ0rlVrhrFSsAacLAjqSqLuMqO+bAbdbZq2xc1wtQk+/xrj1hnRFRJhPqZH5qQetQm8vkQqFg==
   dependencies:
     "@types/estree" "0.0.39"
     acorn "^6.0.5"
@@ -5238,6 +5239,7 @@ js-slang@0.2.0:
     commander "^2.19.0"
     common-tags "^1.8.0"
     invariant "^2.2.4"
+    source-map "^0.7.3"
 
 js-tokens@^3.0.0, js-tokens@^3.0.2:
   version "3.0.2"
@@ -8998,6 +9000,11 @@ source-map@^0.6.0, source-map@^0.6.1, source-map@~0.6.1:
   version "0.6.1"
   resolved "https://registry.yarnpkg.com/source-map/-/source-map-0.6.1.tgz#74722af32e9614e9c287a8d0bbde48b5e2f1a263"
 
+source-map@^0.7.3:
+  version "0.7.3"
+  resolved "https://registry.yarnpkg.com/source-map/-/source-map-0.7.3.tgz#5302f8169031735226544092e64981f751750383"
+  integrity sha512-CkCj6giN3S+n9qrYiBTX5gystlENnRW5jZeNLHpe6aue+SrHcG5VYwujhW9s4dY31mEGsxBDrHR6oI69fTXsaQ==
+
 spdx-correct@^3.0.0:
   version "3.0.0"
   resolved "https://registry.yarnpkg.com/spdx-correct/-/spdx-correct-3.0.0.tgz#05a5b4d7153a195bc92c3c425b69f3b2a9524c82"