diff --git a/js/test_cases/idx_and_len/README.md b/js/test_cases/idx_and_len/README.md
new file mode 100644
index 0000000..c4e8bdd
--- /dev/null
+++ b/js/test_cases/idx_and_len/README.md
@@ -0,0 +1 @@
+$idx and $len seem to only be valid inside sections iterating over arrays, but nothing else.
diff --git a/js/test_cases/idx_and_len/array.json b/js/test_cases/idx_and_len/array.json
new file mode 100644
index 0000000..3f3e0ab
--- /dev/null
+++ b/js/test_cases/idx_and_len/array.json
@@ -0,0 +1,7 @@
+{
+  "things": [
+    "Alice",
+    "Bob",
+    "Chris"
+  ]
+}
diff --git a/js/test_cases/idx_and_len/false.json b/js/test_cases/idx_and_len/false.json
new file mode 100644
index 0000000..d51e741
--- /dev/null
+++ b/js/test_cases/idx_and_len/false.json
@@ -0,0 +1,3 @@
+{
+  "things": false
+}
diff --git a/js/test_cases/idx_and_len/main.dust b/js/test_cases/idx_and_len/main.dust
new file mode 100644
index 0000000..2e645b4
--- /dev/null
+++ b/js/test_cases/idx_and_len/main.dust
@@ -0,0 +1,40 @@
+Outside $idx: {$idx}{~n}
+Outside $len: {$len}{~n}
+Outside {?$idx}$idx is true{:else}$idx is false{/$idx}{~n}
+Outside {?$len}$len is true{:else}$len is false{/$len}{~n}
+
+{#things}
+    Inside Section $idx: {$idx}{~n}
+    Inside Section $len: {$len}{~n}
+    Inside Section {?$idx}$idx is true{:else}$idx is false{/$idx}{~n}
+    Inside Section {?$len}$len is true{:else}$len is false{/$len}{~n}
+{:else}
+    Else Section $idx: {$idx}{~n}
+    Else Section $len: {$len}{~n}
+    Else Section {?$idx}$idx is true{:else}$idx is false{/$idx}{~n}
+    Else Section {?$len}$len is true{:else}$len is false{/$len}{~n}
+{/things}
+
+{?things}
+    Inside Exists $idx: {$idx}{~n}
+    Inside Exists $len: {$len}{~n}
+    Inside Exists {?$idx}$idx is true{:else}$idx is false{/$idx}{~n}
+    Inside Exists {?$len}$len is true{:else}$len is false{/$len}{~n}
+{:else}
+    Else Exists $idx: {$idx}{~n}
+    Else Exists $len: {$len}{~n}
+    Else Exists {?$idx}$idx is true{:else}$idx is false{/$idx}{~n}
+    Else Exists {?$len}$len is true{:else}$len is false{/$len}{~n}
+{/things}
+
+{^things}
+    Inside Not Exists $idx: {$idx}{~n}
+    Inside Not Exists $len: {$len}{~n}
+    Inside Not Exists {?$idx}$idx is true{:else}$idx is false{/$idx}{~n}
+    Inside Not Exists {?$len}$len is true{:else}$len is false{/$len}{~n}
+{:else}
+    Else Not Exists $idx: {$idx}{~n}
+    Else Not Exists $len: {$len}{~n}
+    Else Not Exists {?$idx}$idx is true{:else}$idx is false{/$idx}{~n}
+    Else Not Exists {?$len}$len is true{:else}$len is false{/$len}{~n}
+{/things}
diff --git a/js/test_cases/idx_and_len/number.json b/js/test_cases/idx_and_len/number.json
new file mode 100644
index 0000000..585368a
--- /dev/null
+++ b/js/test_cases/idx_and_len/number.json
@@ -0,0 +1,3 @@
+{
+  "things": 7
+}
diff --git a/js/test_cases/idx_and_len/string.json b/js/test_cases/idx_and_len/string.json
new file mode 100644
index 0000000..90316e2
--- /dev/null
+++ b/js/test_cases/idx_and_len/string.json
@@ -0,0 +1,3 @@
+{
+  "things": "foobar"
+}