1 files changed, 29 insertions, 0 deletions
diff --git a/js/src/jit-test/tests/warp/string-indexof-is-startswith.js b/js/src/jit-test/tests/warp/string-indexof-is-startswith.js
new file mode 100644
index 0000000000..1d9f31e38c
--- /dev/null
+++ b/js/src/jit-test/tests/warp/string-indexof-is-startswith.js
@@ -0,0 +1,29 @@
+// |str.indexOf(searchStr) == 0| is compiled as |str.startsWith(searchStr)|.
+// |str.indexOf(searchStr) != 0| is compiled as |!str.startsWith(searchStr)|.
+
+const strings = [
+  "",
+  "a", "b",
+  "ab", "ba", "ac", "ca",
+  "aba", "abb", "abc", "aca",
+];
+
+function StringIndexOf(str, searchStr) {
+  // Prevent Warp compilation when computing the expected result.
+  with ({});
+  return str.indexOf(searchStr);
+}
+
+for (let str of strings) {
+  for (let searchStr of strings) {
+    let startsWith = str.indexOf(searchStr) === 0;
+
+    assertEq(startsWith, str.startsWith(searchStr));
+    assertEq(startsWith, StringIndexOf(str, searchStr) === 0);
+
+    let notStartsWith = str.indexOf(searchStr) !== 0;
+
+    assertEq(notStartsWith, !str.startsWith(searchStr));
+    assertEq(notStartsWith, StringIndexOf(str, searchStr) !== 0);
+  }
+}