1 files changed, 13 insertions, 0 deletions
diff --git a/js/src/jit-test/tests/warp/string-substring-is-charat.js b/js/src/jit-test/tests/warp/string-substring-is-charat.js
new file mode 100644
index 0000000000..0675aa2029
--- /dev/null
+++ b/js/src/jit-test/tests/warp/string-substring-is-charat.js
@@ -0,0 +1,13 @@
+// |str.substring(0, 1)| is compiled as |str.charAt(0)|.
+
+const strings = [
+  "",
+  "a", "b",
+  "ab", "ba",
+];
+
+for (let i = 0; i < 1000; ++i) {
+  let str = strings[i % strings.length];
+
+  assertEq(str.substring(0, 1), str.charAt(0));
+}