worker to get the data

userWorker.js

export default () => {
  // 'self' instead of 'window'
  self.addEventListener("message", e => {// eslint-disable-line no-restricted-globals
    // the above comment removes the eslint error for self
    
    if (!e) return;
    // the message passed is in e.data
    // we are passing it a json {numberOfUsers: <number>}
    var numberOfUsers = e.data.numberOfUsers;
  
    // function to process the returned data
    var userSelector = function(users) {
      if (Array.isArray(users) && users.length) {
        return users.map(function(d) {
          return {
            name: `${d.name.title} ${d.name.first} ${d.name.last}`,
            address: `${d.location.street.number} ${d.location.street.name}, 
              ${d.location.city}, ${d.location.state}  ${d.location.postcode}`,
            phone: d.phone,
            age: d.dob.age
          };
        });
      }
      return [];
    };
    // fetching the <numberOfUsers> users
    fetch("https://randomuser.me/api/?results=" + numberOfUsers, {
      headers: {
        "Content-Type": "application/json"
      }
    }).then(resp => resp.json())
      .then(data => {
        postMessage(userSelector(data.results));
      })
      .catch(err => {
      // any way you want to handle errors
        postMessage([]);
      });
  });
};