index.ts

import { Format, Loader, transformSync } from 'esbuild'
import path, { extname } from 'path'

const getExt = (str: string) => {
  const basename = path.basename(str);
  const firstDot = basename.indexOf('.');
  const lastDot = basename.lastIndexOf('.');
  const extname = path.extname(basename).replace(/(\.[a-z0-9]+).*/i, '$1');

  if (firstDot === lastDot) return extname

  return basename.slice(firstDot, lastDot) + extname;
}

const getOptions = (config: any) => {
  let options = {}

  for (let i = 0; i < config.transform.length; i++) {
    options = config.transform[i][2]
  }

  return options
}

export interface Options {
  jsxFactory?: string
  jsxFragment?: string
  sourcemap?: boolean | 'inline' | 'external'
  loaders?: {
    [ext: string]: Loader
  },
  target?: string
  format?: string
}

export function process(content: string, filename: string, config: any) {
  const options: Options = getOptions(config)

  const ext = getExt(filename)
  const loader = options?.loaders && options?.loaders[ext] 
    ? options.loaders[ext]
    : extname(filename).slice(1) as Loader

  const sourcemaps = options?.sourcemap 
    ? { sourcemap: true, sourcefile: filename }
    : {}

  const result = transformSync(content, {
    loader,
    format: options?.format as Format || 'cjs',
    target: options?.target || 'es2018',
    ...(options?.jsxFactory ? { jsxFactory: options.jsxFactory }: {}),
    ...(options?.jsxFragment ? { jsxFragment: options.jsxFragment }: {}),
    ...sourcemaps
  })

  return {
    code: result.code,
    map: result?.map ? {
      ...JSON.parse(result.map),
      sourcesContent: null,
    }: ''
  }
}