[TS/JS] Create byte vectors (#8185)

* Add createByteVector and use set in createString

* Add test for CreateByteVector

---------

Co-authored-by: Derek Bailey <derekbailey@google.com>

tests/ts/JavaScriptTest.js

@@ -48,6 +48,7 @@ function main() {
   testNullStrings();
   testSharedStrings();
   testVectorOfStructs();
+  testCreateByteVector();
 
   console.log('FlatBuffers test: completed successfully');
 }
@@ -477,4 +478,20 @@ function testVectorOfStructs() {
   assert.strictEqual(decodedMonster.test4[1].b, 4);
 }
 
+function testCreateByteVector() {
+  const data = Uint8Array.from([1, 2, 3, 4, 5]);
+
+  const builder = new flatbuffers.Builder();
+  const required = builder.createString("required");
+  const offset = builder.createByteVector(data);
+
+  Monster.startMonster(builder);
+  Monster.addName(builder, required);
+  Monster.addInventory(builder, offset)
+  builder.finish(Monster.endMonster(builder));
+
+  let decodedMonster = Monster.getRootAsMonster(builder.dataBuffer());
+  assert.deepEqual(decodedMonster.inventoryArray(), data);
+}
+
 main();

ts/builder.ts

@@ -539,9 +539,24 @@ export class Builder {
       this.addInt8(0);
       this.startVector(1, utf8.length, 1);
       this.bb.setPosition(this.space -= utf8.length);
-      for (let i = 0, offset = this.space, bytes = this.bb.bytes(); i < utf8.length; i++) {
-        bytes[offset++] = utf8[i];
+      this.bb.bytes().set(utf8, this.space);
+      return this.endVector();
+    }
+
+    /**
+     * Create a byte vector.
+     *
+     * @param v The bytes to add
+     * @returns The offset in the buffer where the byte vector starts
+     */
+    createByteVector(v: Uint8Array | null | undefined): Offset {
+      if (v === null || v === undefined) {
+        return 0;
       }
+
+      this.startVector(1, v.length, 1);
+      this.bb.setPosition(this.space -= v.length);
+      this.bb.bytes().set(v, this.space);
       return this.endVector();
     }