Fix repeated `regex.check()` calls on the same regex on target javascript (#459)

3 files changed, 26 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3ce51e9..a5ce2ef 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- Fixed a bug on target JavaScript where `regex.check` would not correctly execute
+  while using the same regular expression in consecutive calls.
 - The `zip` function's second argument in the `list` module gains the `with` label.
 - The `strict_zip` function's second argument in the `list` module gains the `with` label.
 
diff --git a/src/gleam_stdlib.mjs b/src/gleam_stdlib.mjs
index 7c41cdd..1163c6f 100644
--- a/src/gleam_stdlib.mjs
+++ b/src/gleam_stdlib.mjs
@@ -371,6 +371,7 @@ export function utf_codepoint_to_int(utf_codepoint) {
 }
 
 export function regex_check(regex, string) {
+	regex.lastIndex = 0;
   return regex.test(string);
 }
 
diff --git a/test/gleam/regex_test.gleam b/test/gleam/regex_test.gleam
index eb84013..d97c8fa 100644
--- a/test/gleam/regex_test.gleam
+++ b/test/gleam/regex_test.gleam
@@ -27,7 +27,7 @@ pub fn compile_test() {
   regex.check(re, "abc\n123")
   |> should.be_true
 
-  // For Erlang: This test will only passes if unicode and ucp flags are set
+  // On target Erlang this test will only pass if unicode and ucp flags are set
   let assert Ok(re) = regex.compile("\\s", options)
   // Em space == U+2003 == " " == used below
   regex.check(re, " ")
@@ -42,6 +42,28 @@ pub fn check_test() {
 
   regex.check(re, "boo")
   |> should.be_false
+
+  re
+  |> regex.check(content: "foo")
+  |> should.be_true
+
+  "boo"
+  |> regex.check(with: re)
+  |> should.be_false
+
+  // On target JavaScript internal `RegExp` objects are stateful when they
+  // have the global or sticky flags set (e.g., /foo/g or /foo/y).
+  // These following tests make sure that our implementation circumvents this.
+  let assert Ok(re) = regex.from_string("^-*[0-9]+")
+
+  regex.check(re, "1")
+  |> should.be_true
+
+  regex.check(re, "12")
+  |> should.be_true
+
+  regex.check(re, "123")
+  |> should.be_true
 }
 
 pub fn split_test() {