diff --git a/RoboFile.php b/RoboFile.php
index 26d4ae3d10..23adc3325c 100644
--- a/RoboFile.php
+++ b/RoboFile.php
@@ -224,7 +224,7 @@ class RoboFile extends \Robo\Tasks {
   }
 
   public function testJavascript($xmlOutputFile = null) {
-    $command = './node_modules/.bin/mocha --require @babel/register tests/javascript/**/*.spec.js';
+    $command = './node_modules/.bin/mocha --require tests/javascript/babel_register.js  tests/javascript/**/*.spec.js';
 
     if (!empty($xmlOutputFile)) {
       $command .= sprintf(
diff --git a/assets/js/src/form_editor/store/map_form_data_after_loading.jsx b/assets/js/src/form_editor/store/map_form_data_after_loading.jsx
index 45532df8b4..f2a4f4e9e8 100644
--- a/assets/js/src/form_editor/store/map_form_data_after_loading.jsx
+++ b/assets/js/src/form_editor/store/map_form_data_after_loading.jsx
@@ -1,11 +1,4 @@
-function asNum(num) {
-  const numI = parseInt(num, 10);
-  if (Number.isNaN(numI)) {
-    return undefined;
-  }
-  return numI;
-}
-
+import asNum from './server_value_as_num';
 
 export default function mapFormDataAfterLoading(data) {
   return {
diff --git a/assets/js/src/form_editor/store/server_value_as_num.ts b/assets/js/src/form_editor/store/server_value_as_num.ts
new file mode 100644
index 0000000000..bf8f38ef33
--- /dev/null
+++ b/assets/js/src/form_editor/store/server_value_as_num.ts
@@ -0,0 +1,10 @@
+
+function asNum(num?: string): number | undefined {
+  const numI = parseInt(num, 10);
+  if (Number.isNaN(numI)) {
+    return undefined;
+  }
+  return numI;
+}
+
+export default asNum;
diff --git a/package.json b/package.json
index 6b80589d27..ac25fc3d55 100644
--- a/package.json
+++ b/package.json
@@ -18,7 +18,7 @@
     "autoprefixer": "postcss assets/dist/css/*.css --use autoprefixer --no-map --replace",
     "scss": "node-sass assets/css/src/ --output assets/dist/css/ --output-style compact",
     "stylelint": "stylelint --fix",
-    "test": "mocha --require @babel/register tests/javascript/**/*.spec.js",
+    "test": "mocha --require tests/javascript/babel_register.js tests/javascript/**/*.spec.js",
     "check-types": "tsc --noEmit",
     "storybook": "start-storybook -s ./ -p 8083",
     "build-storybook": "build-storybook"
diff --git a/tests/javascript/babel_register.js b/tests/javascript/babel_register.js
new file mode 100644
index 0000000000..7610e62842
--- /dev/null
+++ b/tests/javascript/babel_register.js
@@ -0,0 +1 @@
+require('@babel/register')({ extensions: ['.js', '.jsx', '.ts', '.tsx'] });
diff --git a/tests/javascript/form_editor/store/server_value_as_num.spec.ts b/tests/javascript/form_editor/store/server_value_as_num.spec.ts
new file mode 100644
index 0000000000..d84691d490
--- /dev/null
+++ b/tests/javascript/form_editor/store/server_value_as_num.spec.ts
@@ -0,0 +1,19 @@
+import { expect } from 'chai';
+
+import asNum from '../../../../assets/js/src/form_editor/store/server_value_as_num';
+
+describe.only('Server value as num', () => {
+  it('Converts string to number', () => {
+    expect(asNum('4')).to.equal(4);
+    expect(asNum('0')).to.equal(0);
+    expect(asNum('09')).to.equal(9);
+    expect(asNum('159')).to.equal(159);
+    expect(asNum('-159')).to.equal(-159);
+  });
+
+  it('Converts returns undefined', () => {
+    expect(asNum('xxx')).to.be.undefined;
+    expect(asNum(null)).to.be.undefined;
+    expect(asNum(undefined)).to.be.undefined;
+  });
+});