gistfile1.ts

 interface Worker {
    name: string,
    surname: string,
    deparment: 'ENGINEERING' | 'SALES',
    skills: Array<string>,
 };

 interface Developer extends Worker {
    type: 'FRONT-END' | 'FULL-STACK',
    javascriptLevel: number,
    skills: Array<string>,
  };

  interface SalesRepresantive extends Worker {
    type: 'INTERNATIONAL-SALES' | 'LOCAL-SALES',
    closedDeals: number,
    skills: Array<string>,
  };

  let workers = [
    {
      name: 'James',
      surname: 'Jhonson',
      deparment: 'ENGINEERING',
      type: 'FRONT-END',
      skills: ['ReactJs', 'CSS'],
      javascriptLevel: 8,
    },
    {
      name: 'Adriana',
      surname: 'Lopez',
      deparment: 'SALES',
      type: 'INTERNATIONAL-SALES',
      skills: ['Marketing', 'Writting'],
      closedDeals: 93,
    }
  ];
  
  function isFrontEndDev(worker: Developer | SalesRepresantive): worker is Developer {
    return (worker as Developer).javascriptLevel !== undefined
  };

  let isSalesPerson: Array<SalesRepresantive | Developer> = workers.filter((worker): worker is SalesRepresantive => {
    if(worker.skills.includes('ReactJs')) return false;
    return true;
  });


 let getGihubUsers = async (): Promise<void> => {
    try {
      await fetch('https://api.github.com/users')
        .then(response => response.json())
        .then(users => console.log(users))
    } catch (e) {
      console.error(e)
    }
  }