JavaScript call function after alert box

In the code, the user composes an email by filling out an html form that takes in recipients, subject and body as inputs. I want to display an alert box if the the user didn't provide any recipients. But after clicking OK in the alert box, the inbox.js file re-loads and the user is presented with the "Inbox" mailbox. However, I want them to stay on the compose-mail view instead. I tried to run compose_email function after the alert box but it didn't work. How might I accomplish that?

inbox.js:

document.addEventListener('DOMContentLoaded', function() {

  // Use buttons to toggle between views
  document.querySelector('#inbox').addEventListener('click', () => load_mailbox('inbox'));
  document.querySelector('#sent').addEventListener('click', () => load_mailbox('sent'));
  document.querySelector('#archived').addEventListener('click', () => load_mailbox('archive'));
  document.querySelector('#compose').addEventListener('click', compose_email);

  // By default, load the inbox
  load_mailbox('inbox');
});

function compose_email() {
  // Show compose view and hide other views
  document.querySelector('#display-email').style.display = 'none';
  document.querySelector('#emails-view').style.display = 'none';
  document.querySelector('#compose-view').style.display = 'block';
  // Clear out composition fields
  document.querySelector('#compose-recipients').value = '';
  document.querySelector('#compose-subject').value = '';
  document.querySelector('#compose-body').value = '';

  // Send an Email
  document.querySelector("#compose-form").onsubmit = function(){
    const recipients = document.querySelector("#compose-recipients").value;
    const subject = document.querySelector("#compose-subject").value;
    const body = document.querySelector("#compose-body").value;

    if(recipients.length === 0){
      alert(`At least one recipient is required`);
      compose_email();
    }
    else{
      fetch('/emails', {
      method: 'POST',
      body: JSON.stringify({
          recipients: recipients,
          subject: subject,
          body: body
      })
    })
    .then(response => response.json())
    .then(result => {
        // Print result
        console.log(result);
        if(result[`error`]){
          alert(`User does not exist`)
        }
        else{
          load_mailbox("sent");
        }
    })
    return false;
    }
  }
}