diff --git a/js/tests/primitives_test.js b/js/tests/primitives_test.js
index 28dbf02b..4a4dd9ed 100644
--- a/js/tests/primitives_test.js
+++ b/js/tests/primitives_test.js
@@ -1,5 +1,14 @@
 export const tests = []
+const isConst = (name) => {
+  try {
+    eval(`${name} = 'm'`)
+  return false
+  } catch (err) {
+    return true
+  }
+}
 const t = (f) => tests.push(f)
+
 // str is declared and of type string
 t(() => typeof str === 'string')
 
@@ -12,4 +21,8 @@ t(() => typeof bool === 'boolean')
 // undef is declared and of type undefined
 t(() => undef === undefined)
 
+// check if all variables are const
+t(() => ['str', 'num', 'bool', 'undef']
+  .every(isConst))
+
 Object.freeze(tests)