How to use the @tslab/typescript-for-tslab.ScriptTarget function in @tslab/typescript-for-tslab

cwd,
    options?.isJS ? "__tslab__.js" : "__tslab__.ts"
  );
  const declFilename = pathlib.join(cwd, "__prev__.d.ts");

  const outDir = "outDir";
  const dstFilename = pathlib.join(outDir, "__tslab__.js");
  const dstDeclFilename = pathlib.join(outDir, "__tslab__.d.ts");

  // c.f.
  // https://github.com/microsoft/TypeScript/wiki/Node-Target-Mapping
  // https://github.com/microsoft/TypeScript/issues/22306#issuecomment-412266626
  const traspileTarget =
    semver.major(process.version) >= 12
      ? ts.ScriptTarget.ES2019
      : ts.ScriptTarget.ES2018;

  const srcPrefix = "export {};" + ts.sys.newLine;
  let srcContent: string = "";
  let declContent: string = "";
  /** Check if external .ts files are converted. */
  const sideInputsConverted = new Set();
  let builder: ts.BuilderProgram = null;

  const sys = Object.create(ts.sys) as ts.System;
  let rebuildTimer: RebuildTimer = null;
  sys.getCurrentDirectory = function() {
    return cwd;
  };
  sys.setTimeout = (callback: (...args: any[]) => void): any => {
    if (rebuildTimer) {
      throw new Error("Unexpected pending rebuildTimer");

it("keep named import", () => {
    const src = ts.createSourceFile(
      "src.ts",
      'import mydefault, {foo, bar as baz} from "mylib";',
      ts.ScriptTarget.ES2019
    );
    const stmt = src.statements[0];
    if (!ts.isImportDeclaration(stmt)) {
      fail("stmt is not isImportDeclaration");
      return;
    }
    const names = new Set(["foo"]);
    converter.keepNamesInImport(stmt, names as Set);
    let printer = ts.createPrinter();
    expect(printer.printFile(src)).toEqual('import { foo } from "mylib";\n');
  });

it("wrong names", () => {
    const src = ts.createSourceFile(
      "src.ts",
      'import mydefault, * as ns from "mylib";',
      ts.ScriptTarget.ES2019
    );
    const stmt = src.statements[0];
    if (!ts.isImportDeclaration(stmt)) {
      fail("stmt is not isImportDeclaration");
      return;
    }
    const names = new Set(["wrong"]);
    try {
      converter.keepNamesInImport(stmt, names as Set);
      fail("keepNamesInImport must fail.");
    } catch (e) {
      expect(String(e)).toEqual("Error: no symbol is included in names");
    }
  });
});