Handling HTTP failed request in JavaScript - https://medium.com/douglas-matoso-english/http-primer-for-frontend-developers-f091a2070637

get-fail.js

// the request:
// try to GET an nonexistent URI
fetch('https://api.github.com/nonexistent-uri')
  .then(response => {
    if (response.ok) {
      // we should not reach here
      console.log('success')
    } else {
      console.log(response.status)
    }
  })

// will log:
// 404