@kv-systems/ng-packagr/src/lib/utils/load-esm.ts

Compile and package Angular libraries in Angular Package Format (APF)

export function ngCompilerCli(): Promise<typeof import('@angular/compiler-cli')> {
  return loadEsmModule('@angular/compiler-cli');
}

/**
 * Lazily compiled dynamic import loader function.
 */
let load: (<T>(modulePath: string | URL) => Promise<T>) | undefined;

/**
 * This uses a dynamic import to load a module which may be ESM.
 * CommonJS code can load ESM code via a dynamic import. Unfortunately, TypeScript
 * will currently, unconditionally downlevel dynamic import into a require call.
 * require calls cannot load ESM code and will result in a runtime error. To workaround
 * this, a Function constructor is used to prevent TypeScript from changing the dynamic import.
 * Once TypeScript provides support for keeping the dynamic import this workaround can
 * be dropped.
 *
 * @param modulePath The path of the module to load.
 * @returns A Promise that resolves to the dynamically imported module.
 */
export function loadEsmModule<T>(modulePath: string | URL): Promise<T> {
  load ??= new Function('modulePath', `return import(modulePath);`) as Exclude<typeof load, undefined>;

  return load(modulePath);
}