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Introduction

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Phasis is a pure-PHP JavaScript engine. It lexes, parses, and executes ECMAScript in the host PHP process — without exec('node …'), without FFI, and without a custom binary extension. It requires three standard PHP extensions: ext-mbstring, ext-bcmath and ext-curl (the default fetch() transport). ext-intl and ext-openssl are optional. See Getting Started for builds that leave bcmath out.

  • Embeddable — drop a JS runtime into any PHP app, framework, or CLI tool via the Phasis\Engine class.
  • Spec-compliant — passes the official test262 suite at 100 %, every category, no skips.
  • Web APIs — full Web Platform Pack (URL, TextEncoder/Decoder, atob/btoa, structuredClone, performance, DOMException), full Fetch Pack (fetch, Request, Response, Headers, Body, AbortController/Signal, Blob, File, FormData, EventTarget, full WHATWG Streams, navigator), plus crypto + SubtleCrypto, WebSocket, XMLHttpRequest, and a real event loop. 100 % of imported Web Platform Tests pass.
  • Modern surface — arrow functions, classes, async/await, Promises, generators, Symbol, BigInt, Proxy, Reflect, Temporal, Intl, TypedArrays, full module support.
  • PHP↔JS interop — pass PHP scalars and arrays into JS (arrays are copied), bind PHP closures as JS functions, and call JS functions from PHP. PHP objects cannot be shared with JS yet; see Shared objects.

Why Phasis exists

PHP applications that need to run user-supplied JavaScript — templating engines, frontend SSR shims, data-validation rules, content sandboxes, headless test runners — usually shell out to Node.js or skip the feature. Either path adds operational complexity: a second runtime, a serialization boundary, a network of subprocess pipes, and a hostile deployment story for shared hosting.

Phasis closes that gap. Your PHP code can lex, parse, and execute JavaScript using only PHP 8.2+ with mbstring, bcmath and curl. The engine ships as a Composer package and exposes a single small API surface.

What it does

  • Implements the full ECMAScript standard library: Array, String, Object, Math, JSON, Date, RegExp, Map, Set, Promise, Proxy, Reflect, Symbol, BigInt, TypedArray, Temporal, Intl, generators, async iterators, modules.
  • Ships the Web Platform APIs that real-world JS libraries pre-check for: URL, URLSearchParams, TextEncoder/TextDecoder, atob/btoa, structuredClone, performance, DOMException. See Web APIs for the full surface.
  • Ships fetch with the full Fetch family — Request, Response, Headers, body consumers, AbortController/AbortSignal, Blob, File, FormData, EventTarget/Event, and full WHATWG Streams (ReadableStream, WritableStream, TransformStream, BYOB, queuing strategies). Real HTTP works out of the box via PHP's ext-curl.
  • Ships crypto + full SubtleCrypto (SHA family, HMAC, AES-GCM/CBC/CTR, RSA-OAEP/PSS/PKCS1, ECDSA, ECDH, HKDF, PBKDF2), WebSocket (RFC 6455 + swappable transport), and XMLHttpRequest (layered over the same fetch transport).
  • Ships a real event loop: setTimeout, setInterval, clearTimeout, clearInterval, queueMicrotask, plus Stage-3 AsyncContext for value propagation across async boundaries.
  • Supports modern syntax — destructuring, spread/rest, computed properties, optional chaining, nullish coalescing, template literals, tagged templates, classes (with private fields, static blocks, decorators), top-level await.
  • Converts values across the PHP↔JS boundary. Scalars and arrays are copied in, PHP callables become JS functions, and JS results come back as PHP scalars and arrays. See Value conversion for the exact rules.
  • Runs under host control. The host owns the fetch transport and policy hooks, the event loop runs on virtual time, and a fixed call-stack ceiling stops runaway recursion. A loop-iteration limit exists, but it is not yet enforced on loops the bytecode VM runs, and there are no string-length, output or wall-clock limits; see API: setLimit.
  • Is verified against Node.js (V8). CI runs the unit and oracle suites on every push to main and every pull request, and the Web Platform Tests and popular-package suites when the engine source changes; the full test262 matrix is run by hand and its snapshot committed to COMPAT.md. See Compatibility.

What it is not

Phasis is not a JIT compiler. It is a tree-walking interpreter with an opportunistic bytecode VM. Expect ~100× the runtime of V8 on dispatch-bound workloads. The trade-off is zero dependencies, pure PHP, and host-controlled execution — perfect for embedding JavaScript into PHP apps where correctness and isolation matter more than raw throughput.

Where to start

  • Getting Started — install and run your first script.
  • CLI — bin/phasis for running files, evaluating source, and dumping the AST.
  • API — embed Phasis\Engine in your PHP app.
  • Interop — pass PHP values and callables to JavaScript.
  • Compatibility — test262 coverage and supported features.
  • Parser — parse JavaScript into a typed AST or ESTree without executing it.
  • Formatter — format JavaScript, JSON and CSS with prettier-compatible layout.
  • Advanced — architecture, bytecode VM, benchmarks, and the oracle testing model.