Typescript utils

README.md

Some functions I end up using in just about every js project.

util.ts

/**
 * Type guard for non-empty values. Maintains type information when used with Array.filter
 *
 * Example
 * >>> const a1: number[] = [1, null, 3].filter((e) => !!e) // this compiles with type errors
 * >>> const a2: number[] = [1, null, 3].filter(notEmpty)   // this compiles without
 * @param v any
 */
export const nonEmpty = <T>(v: T | null | undefined): v is T => v !== null && v !== undefined;

export const range = (n: number) => [...new Array(n).keys()];
  
export const sleep = (n: number) => new Promise((r) => setTimeout(r, n));

export function* toGenerator<T>(arr: Array<T>) {
  yield* arr;
}
  
interface poolOptions {
  concurrency: number;
}
const defaultPoolOptions = (): poolOptions => ({
  concurrency: 4,
});
/**
 * Process an async generator concurrently
 * @param resources an async generator
 * @param options
 * @param fn a function to process the generated items
 */
export const withConcurrencyLimit = async <T>(
  resources: Generator<T>,
  options: Partial<poolOptions> = {},
  fn: (arg: T) => Promise<void>
): Promise<void> => {
  const _options = { ...defaultPoolOptions(), options };
  const worker = async () => {
    for await (const r of resources) {
      await fn(r);
    }
  };
  const pool = range(_options.concurrency).map(() => worker());
  await Promise.all(pool);
};