javascript tests and fixes for string.reverse() / string.slice() / string.to_graphemes() (#298)

1 files changed, 26 insertions, 6 deletions

diff --git a/src/gleam/string.gleam b/src/gleam/string.gleam
index 37baed4..45d4d31 100644
--- a/src/gleam/string.gleam
+++ b/src/gleam/string.gleam
@@ -73,10 +73,25 @@ if javascript {
 /// ```
 ///
 pub fn reverse(string: String) -> String {
-  string
-  |> string_builder.from_string
-  |> string_builder.reverse
-  |> string_builder.to_string
+  do_reverse(string)
+}
+
+if erlang {
+  fn do_reverse(string: String) -> String {
+    string
+    |> string_builder.from_string
+    |> string_builder.reverse
+    |> string_builder.to_string
+  }
+}
+
+if javascript {
+  fn do_reverse(string: String) -> String {
+    string
+    |> to_graphemes
+    |> list.reverse
+    |> concat
+  }
 }
 
 /// Creates a new `String` by replacing all occurrences of a given substring.
@@ -233,8 +248,13 @@ if erlang {
 }
 
 if javascript {
-  external fn do_slice(String, Int, Int) -> String =
-    "../gleam_stdlib.mjs" "slice_string"
+  fn do_slice(string: String, idx: Int, len: Int) -> String {
+    string
+    |> to_graphemes
+    |> list.drop(idx)
+    |> list.take(len)
+    |> concat
+  }
 }
 
 /// Drops contents of the first `String` that occur before the second `String`.