GocciaScript

A drop of JavaScript — A sandbox-first ECMAScript runtime implemented in FreePascal

It's based on the thought "What if we implement ECMAScript today, but make the recommended defaults modern, explicit, and sandbox-first". Error-prone, redundant, or high-risk legacy forms are off by default, while the engine and runtime can opt into the compatibility behavior needed for ECMAScript conformance and legacy code. See Language for the full rationale.

Features

GocciaScript implements modern ECMAScript: let/const, arrow functions, classes with private fields, for...of, async/await, ES modules, decorators, and TypeScript-style type annotations. Features that are error-prone, redundant, or security risks (var, function keyword, ==/!=, eval, labels, traditional loops, for...in) are excluded by default; selected legacy forms are available through explicit conformance-focused compatibility flags.

Full ECMAScript compatibility is now a release-track objective. The default language remains curated and sandbox-first, but test262 runs on every PR and main commit so conformance work can be measured from generated reports instead of hand-maintained status claims.

See Language for the complete specification of supported features, TC39 proposals, and exclusions.

Built-in Objects

console, Math, JSON, JSON5, TOML, YAML, JSONL, CSV, TSV, Object, Array, Number, String, RegExp, Symbol, Set, Map, WeakSet, WeakMap, Promise, Temporal, Iterator, Proxy, Reflect, ArrayBuffer, SharedArrayBuffer, TypedArrays (Int8Array, Uint8Array, Uint8ClampedArray, Int16Array, Uint16Array, Int32Array, Uint32Array, Float16Array, Float32Array, Float64Array, BigInt64Array, BigUint64Array) with ArrayBuffer and SharedArrayBuffer backing, fetch, Headers, Response (WHATWG Fetch — GET/HEAD only), URL, URLSearchParams, TextEncoder, TextDecoder, plus error constructors (Error, TypeError, ReferenceError, RangeError, DOMException).

See Built-in Objects for the complete API reference.

Example

class CoffeeShop {
  #name = "Goccia Coffee";
  #beans = ["Arabica", "Robusta", "Ethiopian"];
  #prices = { espresso: 2.5, latte: 4.0, cappuccino: 3.75 };

  getMenu() {
    return this.#beans.map((bean) => `${bean} blend`);
  }

  calculateTotal(order) {
    return order.reduce((total, item) => total + (this.#prices[item] ?? 0), 0);
  }

  get name() {
    return this.#name;
  }
}

const shop = new CoffeeShop();
const order = ["espresso", "latte"];
const total = shop.calculateTotal(order);

console.log(`Welcome to ${shop.name}!`);
console.log(`Your order total: $${total.toFixed(2)}`);

Getting Started

Prerequisites

• FreePascal compiler (fpc)
  • macOS: brew install fpc
  • Ubuntu/Debian: sudo apt-get install fpc
  • Windows: choco install freepascal

Build

# Dev build of everything
./build.pas

# Production build
./build.pas --prod

# Build the script loader only
./build.pas loader

See Build System for build modes, targets, clean builds, and troubleshooting.

Run a Script

./build.pas loader && ./build/GocciaScriptLoader example.js
printf "const x = 2 + 2; x;" | ./build/GocciaScriptLoader --print

By default, both loaders are silent about the script's last evaluated value. Pass --print to emit it; use --output=json for programmatic consumers. See Build System for loader options, bytecode mode, JSON output, sandbox execution, import maps, config files, and resource limits.

Run via Bytecode

GocciaScript includes bytecode execution, and GocciaBundler compiles source to the public .gbc artifact.

./build/GocciaScriptLoader example.js --mode=bytecode
./build/GocciaBundler example.js
./build/GocciaScriptLoader example.gbc

See Bytecode VM for the current bytecode executor architecture.

Start the REPL

./build.pas repl && ./build/GocciaREPL

Run Tests

GocciaScript has 8000+ JavaScript unit tests covering language features, built-in objects, and edge cases.

./build.pas testrunner
./build/GocciaTestRunner tests
./build/GocciaTestRunner tests --mode=bytecode

See Testing for test organization and Build System for runner options.

Run Benchmarks

./build.pas benchmarkrunner && ./build/GocciaBenchmarkRunner benchmarks
./build/GocciaBenchmarkRunner benchmarks/fibonacci.js

The benchmark runner auto-calibrates iterations per benchmark, reports ops/sec with variance (CV%) and engine-level timing breakdown (lex/parse/execute). Output formats: console (default), text, csv, json, compact-json (the same envelope as json without build, memory, stdout, or stderr). Calibration and measurement parameters are configurable via environment variables.

Quick Tour

GocciaScript looks like modern JavaScript — with a few intentional differences:

• Arrow functions only — const greet = (name) => \Hello, ${name}!`;(nofunction` keyword)
• No traditional loops — numbers.map((n) => n * 2) or for (const n of numbers) { ... }
• Classes with private fields — class Account { #balance = 0; ... }
• ES modules — default, named, and namespace imports/exports are supported; project code prefers named exports for clarity.
• Strict equality by default — === and !== (==/!= require --compat-loose-equality)

The CLI tools share WHATWG-style import map support with --import-map=<file.json>, --alias key=value, and automatic goccia.json discovery for project-level module aliases.

Structured data files and text assets can also be imported directly:

import { name, version } from "./package.json";
import { name as packageName } from "./config.toml";
import { name as appName } from "./config.yaml";
import { content, metadata } from "./README.md";

Runtime parsers are available for JSON5, TOML, YAML, JSONL, CSV, and TSV. See Built-in Objects and Language for the full data format reference.

TOML.parse(sourceText) parses TOML 1.1.0 configuration data. YAML.parse(sourceText) handles common configuration files including block scalars, anchors/aliases, merge keys, and YAML 1.2 tag resolution. See Language and Architecture Decision Records for the full conformance details.

JSONL parsing is also available via JSONL.parse(text) and JSONL.parseChunk(text), and .jsonl files can be imported as structured-data modules.

Async/await with full Promise support, including top-level await:

const fetchData = async () => {
  const result = await Promise.resolve({ status: "ok" });
  return result;
};

// Top-level await (ES2022+)
const data = await fetchData();

Strict equality by default — === and !==; == and != are available only with --compat-loose-equality.

For a full guided walkthrough, see the Tutorial. For the complete list of what's supported and excluded, see Language.

Architecture

GocciaScript supports two execution modes that share the same source pipeline (preprocessors, lexer, parser, AST):

flowchart LR
    Source["Source Code"] --> Preprocessors["Preprocessors"] --> Lexer --> Parser --> AST
    AST --> Interpreter["Tree-Walk Interpreter"] --> Result1["Result"]
    AST --> Compiler["Bytecode Compiler"] --> VM["Goccia VM"] --> Result2["Result"]

Loading

Both execution modes share the same value types, built-ins, scope chain, and mark-and-sweep GC. The bytecode executor uses a Goccia-owned VM with tagged TGocciaRegister values (unboxed scalars) that fall back to TGocciaValue for heap objects, not a generic VM layer.

See Architecture for pipelines and layers, Interpreter for tree-walk execution, Bytecode VM for bytecode execution, Core patterns for implementation patterns, and GocciaScript Context for canonical terminology.

Design Principles

• Explicitness: Modules, classes, methods, and properties use explicit, descriptive names even at the cost of verbosity. Shortcuts are avoided.
• OOP over everything: Rely on type safety of specialized classes rather than generic data structures.
• Define vs Assign: Define creates a new variable binding; Assign changes an existing one. These are distinct operations throughout the codebase (see Core patterns).
• Pure evaluation: The evaluator is composed of pure functions with no side effects.
• No global mutable state: All runtime state flows through explicit parameters — the evaluation context, the scope chain, and value objects.
• Virtual dispatch: Property access (GetProperty/SetProperty), type discrimination (IsPrimitive/IsCallable), and scope chain resolution (GetThisValue/GetOwningClass/GetSuperClass) all use virtual methods, replacing type checks with single VMT calls.

See Core patterns and Interpreter for the design rationale.

Documentation

Document	Description
Vision	Why GocciaScript exists: sandboxed AI agent runtime and embeddable desktop platform
Tutorial	Your first GocciaScript program — a guided walkthrough for newcomers
Language	ECMAScript support, recommended defaults, compatibility flags, and rationale
Language Tables	Quick-reference: ECMAScript feature matrix and TC39 proposal status
Built-in Objects	Available built-ins and API reference
Temporal Built-ins	Temporal API: dates, times, durations, time zones
Binary Data Built-ins	ArrayBuffer, SharedArrayBuffer, TypedArray API
Errors	Error types, parser/runtime display, JSON output, Error.cause, try/catch/finally
Architecture	Pipelines, main layers, design direction, duplication boundaries
Interpreter · Bytecode VM	Tree-walk and bytecode execution modes
Core patterns	Recurring implementation patterns
GocciaScript Context	Canonical project terminology and glossary
Value System	Type hierarchy, virtual property access, primitives, objects
Garbage Collector	Mark-and-sweep GC: architecture, contributor rules, design rationale
Adding Built-in Types	Step-by-step guide for adding new built-in types
Embedding the Engine	Embedding GocciaScript in FreePascal applications
Testing	Test organization, running tests, coverage, CI
Test Framework API	Assertions, mocks, lifecycle hooks, async patterns
Benchmarks	Benchmark runner, output formats, writing benchmarks
Build System	Build commands, compiler configuration, CI/CD
Profiling	Bytecode VM profiling: opcodes, functions, output formats
Architecture Decision Records	Durable architectural decisions and trade-offs
Contributing	Single contribution standard: workflow, mandatory rules, testing, FreePascal style
AGENTS.md	Agent operating manual for coding assistants; CONTRIBUTING.md is the contributing guide for everyone

Contributing

CONTRIBUTING.md is the contributing guide for all contributors (humans and AI): workflow, mandatory rules, testing, FreePascal code style, ./format.pas, editor setup, build/run quick reference, and the documentation index.

AGENTS.md (and CLAUDE.md, which points to it) is only for AI assistants—how to use the repo and defer to CONTRIBUTING. It is not a second contributing guide and should stay short.

License

See LICENSE for details.