Do you know why we check for response.ok while using fetch

Take a look at the below code:

fetch('https://jsonplaceholder.typicode.com/todos/4') 
 .then(response => response.json())
 .then(result => console.log('success:',result)) 
 .catch(error => console.log('error:', error));

Here, we’re making an API call to get a todo with id 4 and it will work because there is todo with id 4.

But what If the id does not exist or the server throws an error like 404 or 500 or any other error?

fetch('https://jsonplaceholder.typicode.com/todos/2382822') 
 .then(response => response.json())
 .then(result => console.log('success:',result)) 
 .catch(error => console.log('error:', error));

Here, we have provided a very large id that does not exist. But if you execute in the browser console, you will see that a success message is printed even though it’s clearly a 404 error.

Ideally, the .catch handler should be executed but that does not happen in the case of fetch.

fetch only goes into .catch handler when it fails to make the request for example when the network is not available or the domain does not exist.

So If you’re using fetch for performing the CRUD (create, read, update, delete) operation and the id does not exist then you will get an error.

This is the reason, you will find code for fetch written like this:

fetch('https://jsonplaceholder.typicode.com/todos/4') 
 .then((response) => {
   if (response.ok) { 
    return response.json();
   }
   return Promise.reject(response); 
 })
 .then((result) => { 
   console.log(result); 
 })
 .catch((error) => {
   console.log('Something went wrong.', error); 
 });

where inside the .then handler, we're checking if the response is ok. If the response is ok, we're calling a method that will send the result to the next handler.

If the response is not ok, then we're rejecting the promise so it will call the .catch handler to print the actual error.

That’s it for today.

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