scratch-vm

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

Installation

npm install scratch-vm

Setup

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

// Block events
workspace.addChangeListener(function(e) {
    // Handle "tapping" a block
    if (e instanceof Blockly.Events.Ui && e.element === 'click') {
        var stackBlock = workspace.getBlockById(e.blockId).getRootBlock().id;
        vm.runtime.toggleStack(stackBlock);
    // Otherwise, pass along to the block listener
    } else {
        vm.blockListener(e);
    }
});

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

Standalone Build

make build

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

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!