Since fetch() returns a promise, we can use the catch method of the promise to intercept any error occurring during the execution of the request, and the processing done in the then callbacks:

fetch('./file.json')
.then(response => {
  //...
})
.catch(err => console.error(err))

Another way of catching errors is to manage them in the first then:

fetch('./file.json')
.then(response => {
  if (!response.ok) { throw Error(response.statusText) }
  return response
})
.then(response => {
  //...
})

Lessons in this unit: