Modern sites exchange data with servers: weather, news, products and so on. Those exchanges go through APIs, and JavaScript queries them with fetch.

What is an API?

An API is a service that supplies data on request. You send a request to an address and it sends back a response, usually in JSON format (structured text that code can read easily).

Using fetch

fetch("https://api.exemple.com/donnees")
  .then(reponse => reponse.json())
  .then(donnees => console.log(donnees));

Here is what happens, step by step:

• fetch sends the request to the address you give it.
• .json() turns the response into usable data.
• The second .then finally receives that data so you can work with it.

Because the response can take a while, these operations are asynchronous: the code does not wait around and handles the result as soon as it arrives.

Key takeaway: fetch retrieves remote data through an API. The response comes back later: you handle it with .then.