doc: fix js example of create index (#886)

docs/src/basic.md

@@ -213,8 +213,7 @@ After a table has been created, you can always add more data to it using
 === "Typescript"
 
     ```typescript
-    await tbl.add([{vector: [1.3, 1.4], item: "fizz", price: 100.0},
-                    {vector: [9.5, 56.2], item: "buzz", price: 200.0}])
+    --8<-- "docs/src/basic_legacy.ts:add"
     ```
 
 === "Rust"
@@ -261,7 +260,7 @@ For tables with more than 50K vectors, creating an ANN index is recommended to s
 === "Typescript"
 
     ```{.typescript .ignore}
-    await tbl.createIndex({})
+    --8<-- "docs/src/basic_legacy.ts:create_index"
     ```
 
 === "Rust"

docs/src/basic_legacy.ts

@@ -23,6 +23,23 @@ const example = async () => {
   );
   // --8<-- [end:create_table]
 
+  // --8<-- [start:add]
+  const newData = Array.from({ length: 500 }, (_, i) => ({
+    vector: [i, i + 1],
+    item: "fizz",
+    price: i * 0.1,
+  }));
+  await tbl.add(newData);
+  // --8<-- [end:add]
+
+  // --8<-- [start:create_index]
+  await tbl.createIndex({
+    type: "ivf_pq",
+    num_partitions: 2,
+    num_sub_vectors: 2,
+  });
+  // --8<-- [end:create_index]
+
   // --8<-- [start:create_empty_table]
   const schema = new Schema([
     new Field("id", new Int32()),