Function transform

packages/vite/src/importMetaPlugin.ts:137–209

(code, id, options)

        },

        async transform(code, id, options) {
            if (!isActive || options?.ssr || !includesAlphaTabWorker(code)) {
                return;
            }

            let s: MagicString | undefined;

            // Match `new alphaTabWorker(new ...alphaTabUrl(...))` and any
            // `<expr>.addModule(new ...alphaTabUrl(...))` (the worklet path,
            // which may have its alias inlined away). Worker vs worklet is
            // disambiguated by `getWorkerType` based on the URL string.
            const alphaTabWorkerPattern =
                /\b(alphaTabWorker|[\w.]+\.addModule)\s*\(\s*(new\s+[^ (]+alphaTabUrl\s*\(\s*('[^']+'|"[^"]+"|`[^`]+`)\s*,\s*import\.meta\.url\s*\))/dg;

            let match: RegExpExecArray | null = alphaTabWorkerPattern.exec(code);
            while (match) {
                const workerType = getWorkerType(code, match);

                let typeActive = false;
                switch (workerType) {
                    case AlphaTabWorkerTypes.WorkerClassic:
                    case AlphaTabWorkerTypes.WorkerModule:
                        typeActive = isWorkerActive;
                        break;
                    case AlphaTabWorkerTypes.AudioWorklet:
                        typeActive = isWorkletActive;
                        break;
                }

                if (!typeActive) {
                    match = alphaTabWorkerPattern.exec(code);
                    continue;
                }

                s ??= new MagicString(code);

                const url = code.slice(match.indices![3]![0] + 1, match.indices![3]![1] - 1);

                let file = path.resolve(path.dirname(id), url);
                file =
                    tryFsResolve(file, preserveSymlinks) ??
                    tryOptimizedDepResolve(resolvedConfig, options?.ssr === true, url, id, preserveSymlinks) ??
                    file;

                let builtUrl: string;
                if (isBuild) {
                    builtUrl = await workerFileToUrl(resolvedConfig, file);
                } else {
                    builtUrl = await fileToUrl(cleanUrl(file), resolvedConfig);
                    builtUrl = injectQuery(builtUrl, `${WORKER_FILE_ID}&type=${workerType}`);
                }
                s.update(
                    match.indices![3]![0],
                    match.indices![3]![1],
                    // add `'' +` to skip vite:asset-import-meta-url plugin
                    `new URL('' + ${JSON.stringify(builtUrl)}, import.meta.url)`
                );