scramjet/src/shared/rewriters/js.ts

import { URLMeta } from "./url";

// i am a cat. i like to be petted. i like to be fed. i like to be
import {
	init,
	initSync,
	rewrite_js,
	rewrite_js_from_arraybuffer,
	RewriterOutput,
} from "../../../rewriter/out/rewriter.js";
import { $scramjet, flagEnabled } from "../../scramjet";

initSync({
	module: new WebAssembly.Module(
		Uint8Array.from(atob(self.WASM), (c) => c.charCodeAt(0))
	),
});

init();

Error.stackTraceLimit = 50;

const decoder = new TextDecoder();

function rewriteJsWrapper(
	input: string | ArrayBuffer,
	meta: URLMeta
): string | ArrayBuffer {
	let out: RewriterOutput;
	if (typeof input === "string") {
		out = rewrite_js(
			input,
			meta.base.href,
			"PERCS_PLEASE_FILL_THIS_IN.js",
			$scramjet
		);
	} else {
		out = rewrite_js_from_arraybuffer(
			new Uint8Array(input),
			meta.base.href,
			"PERCS_PLEASE_FILL_THIS_IN.js",
			$scramjet
		);
	}
	const { js, errors, duration } = out;

	// TODO: maybe make this a scram flag?
	if (true) {
		for (const error of errors) {
			console.error("oxc parse error", error);
		}
	}

	// TODO: maybe make this a scram flag?
	if (true) {
		let timespan: string;
		if (duration < 1n) {
			timespan = "BLAZINGLY FAST";
		} else if (duration < 500n) {
			timespan = "decent speed";
		} else {
			timespan = "really slow";
		}
		console.log(`oxc rewrite was ${timespan} (${duration}ms)`);
	}

	return typeof input === "string" ? decoder.decode(js) : js;
}

export function rewriteJs(js: string | ArrayBuffer, meta: URLMeta) {
	if (flagEnabled("naiiveRewriter", meta.origin)) {
		const text = typeof js === "string" ? js : new TextDecoder().decode(js);

		console.log("naiive");

		return rewriteJsNaiive(text);
	}

	js = rewriteJsWrapper(js, meta);

	return js;
}

// 1. does not work with modules
// 2. cannot proxy import()
// 3. disables "use strict" optimizations
// 4. i think the global state can get clobbered somehow
//
// if you can ensure all the preconditions are met this is faster than full rewrites
export function rewriteJsNaiive(js: string | ArrayBuffer) {
	if (typeof js !== "string") {
		js = new TextDecoder().decode(js);
	}

	return `
		with (${$scramjet.config.globals.wrapfn}(globalThis)) {

			${js}

		}
	`;
}