gulpfile.js

const path = require('path');
const gulp = require('gulp');
const through2 = require('through2');
const ts = require('gulp-typescript');
const sourcemaps = require('gulp-sourcemaps');
const merge = require('merge-stream');

const tsConfig = {
  allowJs: true,
  alwaysStrict: true,
  declaration: true,
  esModuleInterop: true,
  forceConsistentCasingInFileNames: true,
  jsx: 'react',
  lib: ['dom', 'es2017'],
  moduleResolution: 'node',
  noFallthroughCasesInSwitch: true,
  noImplicitAny: true,
  noUnusedLocals: true,
  noUnusedParameters: true,
  resolveJsonModule: true,
  skipLibCheck: true,
  strict: true,
  target: 'es5',
  downlevelIteration: true,
};

const tsFiles = ['src/**/*.{ts,tsx}'];

gulp.task('compile', function() {
  const tsResult = gulp
    .src(tsFiles, {
      base: path.join(process.cwd(), 'src'),
    })
    .pipe(sourcemaps.init())
    .pipe(ts(tsConfig));
  return merge(
    tsResult,
    tsResult.js.pipe(
      through2.obj(function(file, encoding, next) {
        console.log(file.path, file.base);
        file.path = file.path.replace(/\.[jt]sx$/, '.js');
        this.push(file);
        next();
      })
    )
  )
    .pipe(sourcemaps.write('.'))
    .pipe(gulp.dest(path.join(process.cwd(), 'lib')));
});