Mock Decorator for angular service

mock-decorator.ts

import {environment} from "../../../environments/environment";

export type ClassConstructor = {new(...args:any[]):{}, prototype: any};

export interface MockingParams<T, K> {
  mockClass: T;
  targetMembers: K[];
  force?: boolean;
}

interface AssignerParams {
  members: (keyof any)[];
  source: any;
  target: any;
}

export function Mock<T extends ClassConstructor>(params: MockingParams<T, keyof InstanceType<T>>) {
  return function mockWith<U extends ClassConstructor>(constructor: U): U {
    if (!isGlobalMockingEnabled() && !params.force) { return constructor; }
    console.log('MOCK', constructor.name);
    assignPrototypeMembers({members: params.targetMembers, source: params.mockClass, target: constructor});
    return constructor;
  }
}

function isGlobalMockingEnabled() {
  return !environment.production && (environment.mock || localStorage.getItem('mock'));
}

function assignPrototypeMembers({members, source, target}: AssignerParams) {
  members.forEach(memberName => {
    if (memberName in target.prototype && memberName in source.prototype) {
      target.prototype[memberName] = source.prototype[memberName];
    } else {
      throw (new Error('Method must exists in both mock class and target class.'))
    }
  })
}

export function enableMockingForAllInLocalStorage() {
  localStorage.setItem('mock', '1');
}

export function disableMockingForAllInLocalStorage() {
  localStorage.removeItem('mock');
}