TypeScriptAsset.js

// node_modules/parcel-bundler/src/assets/TypeScriptAsset.js
const Asset = require('../Asset');
const localRequire = require('../utils/localRequire');
const isAccessedVarChanged = require('../utils/isAccessedVarChanged');
const fs = require('fs');

class TypeScriptAsset extends Asset {
  constructor(name, options) {
    super(name, options);
    this.type = 'js';
    this.cacheData.env = {};
  }

  shouldInvalidate(cacheData) {
    return isAccessedVarChanged(cacheData);
  }

  async generate() {
    // require typescript, installed locally in the app
    let ts = await localRequire('typescript', this.name);
    let transpilerOptions = {
      compilerOptions: {
        module: this.options.scopeHoist
          ? ts.ModuleKind.ESNext
          : ts.ModuleKind.CommonJS,
        jsx: ts.JsxEmit.Preserve,

        // it brings the generated output from TypeScript closer to that generated by Babel
        // see https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-7.html
        esModuleInterop: true
      },
      fileName: this.relativeName
    };

    let tsconfig = await this.getConfig(['tsconfig.json']);

    // Overwrite default if config is found
    if (tsconfig) {
      transpilerOptions.compilerOptions = Object.assign(
        transpilerOptions.compilerOptions,
        tsconfig.compilerOptions
      );
    }
    transpilerOptions.compilerOptions.noEmit = false;
    transpilerOptions.compilerOptions.sourceMap = this.options.sourceMaps;

    // Transpile Module using TypeScript and parse result as ast format through babylon
    let transpiled = ts.transpileModule(
      this.contents,
      transpilerOptions
    );

    // NEW ==============

    const rootFileNames = [this.name];

    const files = {};

    // initialize the list of files
    rootFileNames.forEach(fileName => {
      files[fileName] = { version: 0 };
    });

    console.log(tsconfig);
    const options = tsconfig.compilerOptions;

    const servicesHost = {
      getScriptFileNames: () => rootFileNames,
      getScriptVersion: fileName =>
        files[fileName] && files[fileName].version.toString(),
      getScriptSnapshot: fileName => {
        if (!fs.existsSync(fileName)) {
          return undefined;
        }

        return ts.ScriptSnapshot.fromString(fs.readFileSync(fileName).toString());
      },
      getCurrentDirectory: () => process.cwd(),
      getCompilationSettings: () => options,
      getDefaultLibFileName: options => ts.getDefaultLibFilePath(options),
      fileExists: ts.sys.fileExists,
      readFile: ts.sys.readFile,
      readDirectory: ts.sys.readDirectory,
    };
    const services = ts.createLanguageService(servicesHost, ts.createDocumentRegistry());

    let allDiagnostics = services
      .getCompilerOptionsDiagnostics()
      .concat(services.getSyntacticDiagnostics(this.name))
      .concat(services.getSemanticDiagnostics(this.name));
    allDiagnostics.forEach(diagnostic => {
      let message = ts.flattenDiagnosticMessageText(diagnostic.messageText, "\n");
      if (diagnostic.file) {
        let { line, character } = diagnostic.file.getLineAndCharacterOfPosition(diagnostic.start);
        console.error(`  Error ${diagnostic.file.fileName} (${line + 1},${character +1}): ${message}`);
      } else {
        console.error(`  Error: ${message}`);
      }
    });

    // NEW ==============

    let sourceMap = transpiled.sourceMapText;

    if (sourceMap) {
      sourceMap = JSON.parse(sourceMap);
      sourceMap.sources = [this.relativeName];
      sourceMap.sourcesContent = [this.contents];

      // Remove the source map URL
      let content = transpiled.outputText;
      transpiled.outputText = content.substring(
        0,
        content.lastIndexOf('//# sourceMappingURL')
      );
    }

    return [
      {
        type: 'js',
        value: transpiled.outputText,
        map: sourceMap
      }
    ];
  }
}

module.exports = TypeScriptAsset;