monaco-editor/test/custom-worker.js

// This example uses @typescript/vfs to create a virtual TS program
// which can do work on a bg thread.

importScripts("https://unpkg.com/@typescript/vfs@1.3.0/dist/vfs.globals.js")

/**
 *
 * @param {import("../src/tsWorker").TypeScriptWorker} TypeScriptWorker
 * @param {import("typescript")} ts
 * @param {Record<string, string>} libFileMap
 *
 */
const worker = (TypeScriptWorker, ts, libFileMap) => {
  /** @type { import("@typescript/vfs") } */
  const tsvfs = globalThis.tsvfs

  return class MonacoTSWorker extends TypeScriptWorker {

    // Adds a custom function to the webworker
    async getDTSEmitForFile(fileName) {
      const result = await this.getEmitOutput(fileName)
      const firstDTS = result.outputFiles.find(o => o.name.endsWith(".d.ts"))
      return (firstDTS && firstDTS.text) || ""
    }

    async printAST(fileName) {
      console.log("Creating virtual TS project")
      const compilerOptions = this.getCompilationSettings()
      const fsMap = new Map()
      for (const key of Object.keys(libFileMap)) {
        fsMap.set(key, "/" + libFileMap[key])
      }

      const thisCode =  await this.getScriptText(fileName)
      fsMap.set("index.ts", thisCode)

      console.log("Starting up TS program")
      const system = tsvfs.createSystem(fsMap)
      const host = tsvfs.createVirtualCompilerHost(system, compilerOptions, ts)

      const program = ts.createProgram({
        rootNames: [...fsMap.keys()],
        options: compilerOptions,
        host: host.compilerHost,
      })

      // Now I can look at the AST for the .ts file too
      const mainSrcFile = program.getSourceFile("index.ts")
      let miniAST = "SourceFile"

      const recurse = (parent, depth) => {
        if (depth > 5) return
        ts.forEachChild(parent, node => {
          const spaces = "  ".repeat(depth + 1)
          miniAST += `\n${spaces}${ts.SyntaxKind[node.kind]}`
          recurse(node, depth + 1)
        })
      }
      recurse(mainSrcFile, 0)
      return miniAST
    }

  }
}

self.customTSWorkerFactory = worker