JavaScript Function: Fetching data from API with request timeout

JavaScript Asynchronous: Exercise-9 with Solution

Write a JavaScript function that fetches data from an API and cancels the request if it takes longer than a specified time.

Sample Solution:

JavaScript Code:

function fetchDataWithTimeout(url, timeout) {
  const controller = new AbortController();
  const { signal } = controller;

  const timeoutId = setTimeout(() => {
    controller.abort();
  }, timeout);

  return fetch(url, { signal })
    .then(response => {
      clearTimeout(timeoutId);
      if (!response.ok) {
        throw new Error(`HTTP error! Status: ${response.status}`);
      }
      return response.json();
    })
    .catch(error => {
      if (error.name === 'AbortError') {
        throw new Error('Request timed out.');
      } else {
        throw error;
      }
    });
}
// Usage example:
const url = 'https://jsonplaceholder.typicode.com/posts/1';
const timeoutMs = 5000;  
//const timeoutMs = 50;  
console.log("Timeout milliseconds: "+timeoutMs)

fetchDataWithTimeout(url, timeoutMs)
  .then(data => {
    console.log('Data:', data);
  })
  .catch(error => {
    console.log('Error:', error.message);
  });

Output:

 "Timeout milliseconds: 5000"
"Data:"
[object Object] {
  body: "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto",
  id: 1,
  title: "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
  userId: 1
}

"Timeout milliseconds: 50"
"Error:"
"Request timed out."

Note: Executed on JS Bin

Explanation:

In the above exercise -

• The function "fetchDataWithTimeout()" takes two parameters: url (the URL to fetch data from) and timeout (the maximum time in milliseconds allowed for the request).
• It creates an 'AbortController' instance and obtains its associated signal. The 'AbortController' cancels the request if it exceeds the specified timeout.
• A timeout is set using setTimeout, which calls controller.abort() when the specified timeout duration elapses. This cancels the request by aborting it.
• The function uses the fetch API to make the actual request, passing the signal to the options object to associate it with the request.
• If the response is successful (response.ok is true), the function clears the timeout using clearTimeout(timeoutId) and parses the response data as JSON using response.json().
• If the response is not successful, an error is thrown with a message indicating HTTP error status.
• If an error occurs during the request, the function checks if the error name is 'AbortError', which indicates that the request was aborted due to a timeout. In this case, it throws an error with the message "Request timed out." Otherwise, it rethrows the original error.
• The function returns a Promise that resolves with the parsed response data or rejects with an error.

In the usage example, the "fetchDataWithTimeout()" function is called with a sample URL and a timeout of 5000 milliseconds and 50 milliseconds. The fetched data is logged if the request is successful, and any errors are caught and logged.

Flowchart:

Live Demo:

See the Pen javascript-asynchronous-exercise-9 by w3resource (@w3resource) on CodePen.

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