Function polyfillsPlugin

packages/plugin-legacy/src/index.ts:973–993

(
  imports: Set<string>,
  excludeSystemJS?: boolean,
)

const polyfillId = '\0vite/legacy-polyfills'

function polyfillsPlugin(
  imports: Set<string>,
  excludeSystemJS?: boolean,
): Plugin {
  return {
    name: 'vite:legacy-polyfills',
    resolveId(id) {
      if (id === polyfillId) {
        return id
      }
    },
    load(id) {
      if (id === polyfillId) {
        return (
          [...imports].map((i) => `import ${JSON.stringify(i)};`).join('') +
          (excludeSystemJS ? '' : `import "systemjs/dist/s.min.js";`)
        )
      }
    },
  }
}

function prependModenChunkLegacyGuardPlugin(): Plugin {
  let sourceMapEnabled!: boolean