make `regex.scan`'s behavior consistent across targets (#423)

1 files changed, 11 insertions, 2 deletions

diff --git a/src/gleam_stdlib.mjs b/src/gleam_stdlib.mjs
index 37c3ea2..632c668 100644
--- a/src/gleam_stdlib.mjs
+++ b/src/gleam_stdlib.mjs
@@ -388,8 +388,17 @@ export function compile_regex(pattern, options) {
 
 export function regex_scan(regex, string) {
   let matches = Array.from(string.matchAll(regex)).map((match) => {
-    let content = match.shift();
-    let submatches = match.map((x) => (x ? new Some(x) : new None()));
+    const content = match[0];
+    const submatches = [];
+    for (let n = match.length - 1; n > 0; n--) {
+      if (match[n]) {
+        submatches[n-1] = new Some(match[n])
+        continue
+      }
+      if(submatches.length > 0) {
+        submatches[n-1] = new None()
+      }
+    }
     return new RegexMatch(content, List.fromArray(submatches));
   });
   return List.fromArray(matches);