Use in TypeScript    {#flatbuffers_guide_use_typescript}
=================

## Before you get started

Before diving into the FlatBuffers usage in TypeScript, it should be noted that
the [Tutorial](../tutorial.md) page has a complete guide to
general FlatBuffers usage in all of the supported languages
(including TypeScript). This page is specifically designed to cover the nuances
of FlatBuffers usage in TypeScript.

You should also have read the [Building](../building.md)
documentation to build `flatc` and should be familiar with
[Using the schema compiler](../flatc.md) and
[Writing a schema](../schema.md).

## FlatBuffers TypeScript library code location

The code for the FlatBuffers TypeScript library can be found at
https://www.npmjs.com/package/flatbuffers.

## Testing the FlatBuffers TypeScript library

To run the tests, use the [TypeScriptTest.py](https://github.com/google/
flatbuffers/blob/master/tests/TypeScriptTest.py) Python3 script.

*Note: The TypeScript test file requires [Node.js](https://nodejs.org/en/).*

## Using the FlatBuffers TypeScript library

*Note: See [Tutorial](../tutorial.md) for a more in-depth
example of how to use FlatBuffers in TypeScript.*

FlatBuffers supports both reading and writing FlatBuffers in TypeScript.

To use FlatBuffers in your own code, first generate TypeScript classes from your
schema with the `--ts` option to `flatc`. Then you can include both FlatBuffers
and the generated code to read or write a FlatBuffer.

For example, here is how you would read a FlatBuffer binary file in TypeScript:
First, include the library and generated code. Then read the file into an
`Uint8Array`. Make a `flatbuffers.ByteBuffer` out of the `Uint8Array`, and pass
the ByteBuffer to the `getRootAsMonster` function.

~~~{.ts}
  import * as flatbuffers from 'flatbuffers';

  import { MyGame } from './monster_generated';

  let data = new Uint8Array(fs.readFileSync('monster.dat'));
  let buf = new flatbuffers.ByteBuffer(data);

  let monster = MyGame.Example.Monster.getRootAsMonster(buf);
~~~

Now you can access values like this:

~~~{.ts}
  let hp = monster.hp();
  let pos = monster.pos();
~~~

## Object based API

FlatBuffers is all about memory efficiency, which is why its base API is written
around using as little as possible of it. This does make the API clumsier
(requiring pre-order construction of all data, and making mutation harder).

For times when efficiency is less important a more convenient object based API
can be used (through `--gen-object-api`) that is able to unpack & pack a
FlatBuffer into objects and standard TS types.

To use:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.ts}
    // Autogenerated class from table Monster.
    let monsterobj = new MonsterT();

    // Deserialize from buffer into object.
    Monster.getRootAsMonster(flatbuffer).unpackTo(monsterobj);
    // or
    let monsterobj = Monster.getRootAsMonster(flatbuffer).unpack();

    // Update object directly like a regular TS class instance.
    console.log(monsterobj.name);
    monsterobj.name = "Bob";

    // Serialize into new flatbuffer.
    let fbb = new flatbuffers.Builder(1);
    Monster.finishMonsterBuffer(fbb, monsterobj.pack(fbb));
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

## Text parsing FlatBuffers in TypeScript

There currently is no support for parsing text (Schema's and JSON) directly
from TypeScript.
