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Use in JavaScript

Before you get started

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

You should also have read the Building documentation to build flatc and should be familiar with Using the schema compiler and Writing a schema.

FlatBuffers JavaScript library code location

The code for the FlatBuffers JavaScript library can be found at flatbuffers/js. You can browse the library code on the FlatBuffers GitHub page.

Testing the FlatBuffers JavaScript library

The code to test the JavaScript library can be found at flatbuffers/tests. The test code itself is located in JavaScriptTest.js.

To run the tests, use the JavaScriptTest.sh shell script.

Note: The JavaScript test file requires Node.js.

Using the FlatBuffers JavaScript libary

Note: See Tutorial for a more in-depth example of how to use FlatBuffers in JavaScript.

FlatBuffers supports both reading and writing FlatBuffers in JavaScript.

To use FlatBuffers in your own code, first generate JavaScript classes from your schema with the --js 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 Javascript: 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.

Note: Both JavaScript module loaders (e.g. Node.js) and browser-based HTML/JavaScript code segments are shown below in the following snippet:

// Note: These require functions are specific to JavaScript module loaders
// (namely, Node.js). See below for a browser-based example.
var fs = require('fs');
var flatbuffers = require('../flatbuffers').flatbuffers;
var MyGame = require('./monster_generated').MyGame;
var data = new Uint8Array(fs.readFileSync('monster.dat'));
var buf = new flatbuffers.ByteBuffer(data);
var monster = MyGame.Example.Monster.getRootAsMonster(buf);
// Note: This code is specific to browser-based HTML/JavaScript. See above
// for the code using JavaScript module loaders (e.g. Node.js).
<script src="../js/flatbuffers.js"></script>
<script src="monster_generated.js"></script>
function readFile() {
var reader = new FileReader(); // This example uses the HTML5 FileReader.
var file = document.getElementById(
'file_input').files[0]; // "monster.dat" from the HTML <input> field.
reader.onload = function() { // Executes after the file is read.
var data = new Uint8Array(reader.result);
var buf = new flatbuffers.ByteBuffer(data);
var monster = MyGame.Example.Monster.getRootAsMonster(buf);
// Open the HTML file in a browser and select "monster.dat" from with the
// <input> field.
<input type="file" id="file_input" onchange="readFile();">

Now you can access values like this:

var hp = monster.hp();
var pos = monster.pos();

Text parsing FlatBuffers in JavaScript

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