Virtual Machine used to represent, run, and maintain the state of programs for Scratch 3.0
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scratch-vm

Scratch VM is a library for representing, running, and maintaining the state of computer programs written using Scratch Blocks.

Build Status Dependency Status devDependency Status

Installation

This requires you to have Git and Node.js installed.

In your own node environment/application:

npm install https://github.com/LLK/scratch-vm.git

If you want to edit/play yourself:

git clone git@github.com:LLK/scratch-vm.git
cd scratch-vm
npm install

Development Server

This requires Node.js to be installed.

For convenience, we've included a development server with the VM. This is useful because the VM can take advantage of executing in a WebWorker, which is not permitted in a local file.

Running the Development Server

Open a Command Prompt or Terminal in the repository and run:

npm start

Or on Windows:

StartServerWindows.bat

Playground

To run the Playground, make sure the dev server's running and go to http://localhost:8080/ - you will be redirected to the playground, which demonstrates various tools and internal state.

VM Playground Screenshot

Standalone Build

make build
<script src="/path/to/vm.js"></script>
<script>
    var vm = new window.VirtualMachine();
    // do things
</script>

How to include in a Node.js App

For an extended setup example, check out the /playground directory, which includes a fully running VM instance.

var VirtualMachine = require('scratch-vm');
var vm = new VirtualMachine();

// Block events
workspace.addChangeListener(vm.blockListener);
var flyoutWorkspace = workspace.toolbox_.flyout_.workspace_;
flyoutWorkspace.addChangeListener(vm.flyoutBlockListener);

// Run threads
vm.runtime.start();

Abstract Syntax Tree

Overview

The Virtual Machine constructs and maintains the state of an Abstract Syntax Tree (AST) by listening to events emitted by the scratch-blocks workspace via the blockListener. At any time, the current state of the AST can be viewed by inspecting the vm.runtime.blocks object.

Anatomy of a Block

{
    "7AJZR#NA;m*b}R]pdq63": {
      "id": "7AJZR#NA;m*b}R]pdq63",
      "opcode": "control_wait",
      "inputs": {
        "DURATION": {
          "name": "DURATION",
          "block": ",xA8/S!Z6+kR,9dph.rO"
        }
      },
      "fields": {},
      "next": null,
      "topLevel": true
    },
    ",xA8/S!Z6+kR,9dph.rO": {
      "id": ",xA8/S!Z6+kR,9dph.rO",
      "opcode": "math_number",
      "inputs": {},
      "fields": {
        "NUM": {
          "name": "NUM",
          "value": "1"
        }
      },
      "next": null,
      "topLevel": false
    }
  }

Testing

make test
make coverage

Donate

We provide Scratch free of charge, and want to keep it that way! Please consider making a donation to support our continued engineering, design, community, and resource development efforts. Donations of any size are appreciated. Thank you!