What exactly is the second parameter that the fetch API takes?

Question

I went to MDN and read about the fetch API and it says:

You can also optionally pass in an init options object as the second argument

Suppose, we have this simple login function:

const login = () => {
    const requestOptions = {
        method: "POST",
        headers: { "Content-type": "application/json" },
        body: JSON.stringify({ username, password })
    }

    return fetch(`apiUrl/users/authenticate`, requestOptions)
        .then(res = res.json)
            .then(data => console.log(data))
}

So, requestOptions is an init object here?

Answer 1

Init object is the options with which you can initialize the fetch methods. The below are the most commonly used options that you can pass to fetch as in init object.

  1. method: 'POST', // *GET, POST, PUT, DELETE, etc.
  2. mode: 'cors', // no-cors, *cors, same-origin
  3. cache: 'no-cache', // *default, no-cache, reload, force-cache, only-if-cached
  4. credentials: 'same-origin', // include, *same-origin, omit
  5. headers: {
    'Content-Type': 'application/json'
    // 'Content-Type': 'application/x-www-form-urlencoded',
  },
  7. redirect: 'follow', // manual, *follow, error
  8. referrerPolicy: 'no-referrer', // no-referrer, *client
  9. body: JSON.stringify(data) // body data type must match "Content-Type" header

You can read more bout this on MDN