other components... (2)

src/validation/alfanum.ts

@@ -0,0 +1,13 @@
+export function alfanum(username: string) {
+  let code, i, len
+
+  for (i = 0, len = username.length; i < len; i++) {
+    code = username.charCodeAt(i)
+    if (!(code > 47 && code < 58) && // numeric (0-9)
+      !(code > 64 && code < 91) && // upper alpha (A-Z)
+      !(code > 96 && code < 123)) { // lower alpha (a-z)
+      return false
+    }
+  }
+  return true
+}