Fetch, the native method to do ajax

Posted on April 30, 2019 in
2 min read

Everybody knows that one of the most important benefits of jQuery has always been the $.get() or the $.ajax() function to perform the so-called ajax request in the browser. At that time doing the same in vanilla js (using the XMLHttpRequest object) was way more verbose and error-prone.

Nowadays, the modern javascript provides us a much modern method to perform http requests.

Fetch, the modern native function looks pretty much the predecessor of jQuery or other libraries such as d3 and axios.

Its usage is pretty straightforward, well documented on the MDN website.

Unlike the libraries that have similar fetch concepts, the native fetch returns a Promise of the request first, then a second Promise will contain the response of the server.

So, a request made with jQuery, like:

    .then(data => console.log(data))

should be rewritten using fetch like:

    .then(response => response.json())
    .then(data => console.log(data))

The .json() function actually convert the raw data into a native javascript object, that object will be returned by the second Promise.

To catch an error, use the .catch function as usual in this type of context:

    .then(response => response.json())
    .then(data => console.log(data))
    .catch(err => console.log(err))

Fetch options

For instance, to perform a POST request with fetch, here the way:

fetch(`/save`, {
      method: 'POST',
      body: JSON.stringify({ }),
      headers: {
        'Content-Type': 'application/json'
    .then(response => response.json())
    .then(data => console.log(data))
    .catch(err => console.log(err))

You have to add on optional configuration object where you can specify the method and other options as well.

At first sight the double Promises to get the data we want looks a bit over-complicated and unnecessary.

In reality, using the async/await keywords, the possibility to separate the response status and the actual server response is essential to catch all the edge cases.

Stay tuned for the next tip about them.