Enumerate keys/elements and pagination

packages/near-contract-standards/src/non_fungible_token/impl.ts

@@ -115,8 +115,8 @@ export class NonFungibleToken
     assert(l > 0, "limit must be greater than 0.");
     l = Math.min(l, this.owner_by_id.length - start_index);
     const ret: Token[] = [];
-    for (let i = start_index; i < start_index + l; i++) {
-      const token_id = this.owner_by_id.keys.get(i);
+    const tokens = this.owner_by_id.keys({start: from_index, limit: l});
+    for (let token_id of tokens) {
       const owner_id = this.owner_by_id.get(token_id);
       ret.push(this.enum_get_token(owner_id, token_id));
     }
@@ -165,8 +165,8 @@ export class NonFungibleToken
     l = Math.min(l, token_set.length - start_index);
 
     const ret: Token[] = [];
-    for (let i = start_index; i < start_index + l; i++) {
-      const token_id = token_set.elements.get(i);
+    const tokens = token_set.elements({start: from_index, limit: l});
+    for (let token_id of tokens) {
       const owner_id = this.owner_by_id.get(token_id);
       ret.push(this.enum_get_token(owner_id, token_id));
     }