Typescript Generic Helpers

generic-helpers.ts

export const isString = (obj: unknown) =>
  obj !== undefined
  && obj !== null
  && (obj instanceof String || typeof obj === 'string');

export const isNone = (v?: unknown): boolean => v === undefined || v === null;
export const isUndefined = (v?: unknown): boolean => v === undefined;
export const isBool = val => 'boolean' === typeof val;

export const asBool = (v?: unknown): boolean =>
    isBool(v) ? v :
        ((isString(v) && v.toLowerCase() === 'true')
            || (Number.isFinite(v) && v > 0));

export const lowerCase = (str: string): string =>
    str.toString().toLowerCase()

export const groupBy = <T, K extends keyof any>(arr: T[], key: (i: T) => K) =>
  arr.reduce((groups, item) => {
    (groups[key(item)] ||= []).push(item);
    return groups;
  }, {} as Record<K, T[]>);