diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0fc4b98e4..0c8f567a8 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,5 +1,8 @@
 name: CI
 
+defaults:
+  run: {shell: bash}
+
 env:
   # Run on Node 14 because node-fibers doesn't support odd-numbered Node
   # versions. Note: when changing this, also change
@@ -14,8 +17,8 @@ on:
   pull_request:
 
 jobs:
-  sass_spec:
-    name: "sass-spec | Dart ${{ matrix.dart_channel }} | ${{ matrix.async_label }}"
+  sass_spec_language:
+    name: "Language Tests | Dart ${{ matrix.dart_channel }} | ${{ matrix.async_label }}"
     runs-on: ubuntu-latest
 
     strategy:
@@ -34,13 +37,8 @@ jobs:
       - uses: dart-lang/setup-dart@v1
         with: {sdk: "${{ matrix.dart_channel }}"}
       - run: dart pub get
-      # Set up the environment to run the sass-spec runner which is written in Ruby
       - name: Set up sass-spec
-        run: |
-          export sass_spec_ref=`tool/github-action/sass-spec-ref.sh`
-          git init sass-spec
-          git -C sass-spec fetch git://github.com/sass/sass-spec "$sass_spec_ref" --depth 1
-          git -C sass-spec checkout FETCH_HEAD
+        run: tool/github-action/check-out-sass-spec.sh
         env:
           PR_BRANCH: "${{ github.base_ref }}"
           CURRENT_REF: "${{ github.ref }}"
@@ -54,6 +52,60 @@ jobs:
         working-directory: sass-spec
         env: {extra_args: "${{ matrix.async_args }}"}
 
+  # The versions should be kept up-to-date with the latest LTS Node releases.
+  # They next need to be rotated April 2021. See
+  # https://github.com/nodejs/Release.
+  sass_spec_js:
+    name: "JS API Tests | Dart ${{ matrix.dart_channel }} | Node ${{ matrix.node_version }} | ${{ matrix.os }}"
+    runs-on: "${{ matrix.os }}"
+
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+        dart_channel: [stable]
+        node_version: [14]
+        include:
+          # Include LTS versions on Ubuntu
+          - os: ubuntu-latest
+            dart_channel: stable
+            node_version: 12
+          - os: ubuntu-latest
+            dart_channel: stable
+            node_version: 10
+          - os: ubuntu-latest
+            dart_channel: dev
+            node_version: 14
+
+    steps:
+      - uses: actions/checkout@v2
+      - uses: dart-lang/setup-dart@v1
+        with: {sdk: "${{ matrix.dart_channel }}"}
+      - run: dart pub get
+      - uses: actions/setup-node@v2
+        with: {node-version: "${{ matrix.node_version }}"}
+
+      - name: Check out sass-spec
+        run: tool/github-action/check-out-sass-spec.sh
+        env:
+          PR_BRANCH: "${{ github.base_ref }}"
+          CURRENT_REF: "${{ github.ref }}"
+          PR_BODY: "${{ github.event.pull_request.body }}"
+
+      - name: Build JS
+        run: dart pub run grinder pkg-npm-dev
+
+      - name: Link Dart Sass into sass-spec
+        run: npm install ../build/npm
+        working-directory: sass-spec
+
+      - name: Check out Sass specification
+        run: git clone https://github.com/sass/sass.git language --depth 1
+
+      - name: Run tests
+        run: npm run js-api-spec -- --sassSassRepo ../language
+        working-directory: sass-spec
+
   dart_tests:
     name: "Dart tests | Dart ${{ matrix.dart_channel }} | ${{ matrix.os }}"
     runs-on: "${{ matrix.os }}"
@@ -142,10 +194,16 @@ jobs:
           --errors ambiguous-doc-reference,broken-link,deprecated
           --errors unknown-directive,unknown-macro,unresolved-doc-reference
 
-  sanity_checks:
-    name: Sanity checks
+  double_check:
+    name: Double-check
     runs-on: ubuntu-latest
-    needs: [sass_spec, dart_tests, node_tests, static_analysis, dartdoc]
+    needs:
+    - sass_spec_language
+    - sass_spec_js
+    - dart_tests
+    - node_tests
+    - static_analysis
+    - dartdoc
     if: "startsWith(github.ref, 'refs/tags/') && github.repository == 'sass/dart-sass'"
 
     steps:
@@ -158,7 +216,7 @@ jobs:
   deploy_github_linux:
     name: "Deploy Github: Linux"
     runs-on: ubuntu-latest
-    needs: [sanity_checks]
+    needs: [double_check]
     if: "startsWith(github.ref, 'refs/tags/') && github.repository == 'sass/dart-sass'"
 
     steps:
@@ -206,7 +264,7 @@ jobs:
   deploy_npm:
     name: Deploy npm
     runs-on: ubuntu-latest
-    needs: [sanity_checks]
+    needs: [double_check]
     if: "startsWith(github.ref, 'refs/tags/') && github.repository == 'sass/dart-sass'"
 
     steps:
@@ -241,7 +299,7 @@ jobs:
   deploy_pub:
     name: "Deploy Pub"
     runs-on: ubuntu-latest
-    needs: [sanity_checks]
+    needs: [double_check]
     if: "startsWith(github.ref, 'refs/tags/') && github.repository == 'sass/dart-sass'"
 
     steps:
@@ -274,7 +332,7 @@ jobs:
   deploy_homebrew:
     name: "Deploy Homebrew"
     runs-on: ubuntu-latest
-    needs: [sanity_checks]
+    needs: [double_check]
     if: "startsWith(github.ref, 'refs/tags/') && github.repository == 'sass/dart-sass'"
 
     steps:
@@ -290,7 +348,7 @@ jobs:
   deploy_chocolatey:
     name: "Deploy Chocolatey"
     runs-on: windows-latest
-    needs: [sanity_checks]
+    needs: [double_check]
     if: "startsWith(github.ref, 'refs/tags/') && github.repository == 'sass/dart-sass'"
 
     steps:
@@ -304,7 +362,7 @@ jobs:
   deploy_website:
     name: "Deploy sass-lang.com"
     runs-on: ubuntu-latest
-    needs: [sanity_checks]
+    needs: [double_check]
     if: "startsWith(github.ref, 'refs/tags/') && github.repository == 'sass/dart-sass'"
 
     steps:
diff --git a/tool/github-action/check-out-sass-spec.sh b/tool/github-action/check-out-sass-spec.sh
new file mode 100755
index 000000000..8dd941df3
--- /dev/null
+++ b/tool/github-action/check-out-sass-spec.sh
@@ -0,0 +1,47 @@
+#!/bin/bash -e
+# Copyright 2016 Google Inc. Use of this source code is governed by an MIT-style
+# license that can be found in the LICENSE file or at
+# https://opensource.org/licenses/MIT.
+
+# Echoes the sass-spec Git ref that should be checked out for the current GitHub
+# Actions run. If we're running specs for a pull request which refers to a
+# sass-spec pull request, we'll run against the latter rather than sass-spec
+# main.
+function choose-ref() {
+  if [ -z "$PR_BRANCH" ]; then
+    # Remove the "refs/heads/" prefix
+    current_branch="${CURRENT_REF:11}"
+  else
+    current_branch="$PR_BRANCH"
+  fi
+
+  if [[ "$current_branch" == feature.* ]]; then
+    default="$current_branch"
+  else
+    default=main
+  fi
+
+  # We don't have a PR_BRANCH so we are not in a pull request
+  if [ -z "$PR_BRANCH" ]; then
+    >&2 echo "Ref: $default."
+    echo "$default"
+    exit 0
+  fi
+
+  >&2 echo "$PR_BODY"
+
+  RE_SPEC_PR="sass/sass-spec(#|/pull/)([0-9]+)"
+
+  if [[ "$PR_BODY" =~ $RE_SPEC_PR ]]; then
+    ref="pull/${BASH_REMATCH[2]}/head"
+    >&2 echo "Ref: $ref."
+    echo "$ref"
+  else
+    >&2 echo "Ref: $default."
+    echo "$default"
+  fi
+}
+
+git init sass-spec
+git -C sass-spec fetch git://github.com/sass/sass-spec "$(choose-ref)" --depth 1
+git -C sass-spec checkout FETCH_HEAD
diff --git a/tool/github-action/sass-spec-ref.sh b/tool/github-action/sass-spec-ref.sh
deleted file mode 100755
index 069c0900b..000000000
--- a/tool/github-action/sass-spec-ref.sh
+++ /dev/null
@@ -1,42 +0,0 @@
-#!/bin/bash -e
-# Copyright 2016 Google Inc. Use of this source code is governed by an MIT-style
-# license that can be found in the LICENSE file or at
-# https://opensource.org/licenses/MIT.
-
-# Echoes the sass-spec Git ref that should be checked out for the current GitHub
-# Actions run. If we're running specs for a pull request which refers to a
-# sass-spec pull request, we'll run against the latter rather than sass-spec
-# main.
-
-if [ -z "$PR_BRANCH" ]; then
-  # Remove the "refs/heads/" prefix
-  current_branch="${CURRENT_REF:11}"
-else
-  current_branch="$PR_BRANCH"
-fi
-
-if [[ "$current_branch" == feature.* ]]; then
-  default="$current_branch"
-else
-  default=main
-fi
-
-# We don't have a PR_BRANCH so we are not in a pull request
-if [ -z "$PR_BRANCH" ]; then
-  >&2 echo "Ref: $default."
-  echo "$default"
-  exit 0
-fi
-
->&2 echo "$PR_BODY"
-
-RE_SPEC_PR="sass/sass-spec(#|/pull/)([0-9]+)"
-
-if [[ "$PR_BODY" =~ $RE_SPEC_PR ]]; then
-  ref="pull/${BASH_REMATCH[2]}/head"
-  >&2 echo "Ref: $ref."
-  echo "$ref"
-else
-  >&2 echo "Ref: $default."
-  echo "$default"
-fi