Mock `router` to test component using Jest

function fetchData() {
  return new Promise((resolve, reject) => {
    // Asynchronous operation
    setTimeout(() => {
      const data = 'Some data';
      if (data) {
        resolve(data);
      } else {
        reject('Error: Data not found');
      }
    }, 1000);
  });
}

fetchData()
  .then((data) => {
    console.log(data);
  })
  .catch((error) => {
    console.error(error);
  });

By wrapping the asynchronous operation in a Promise, we can use the then method to handle the resolved value and the catch method to handle any errors. This approach makes the code more readable and manageable compared to nested callbacks.

Problem 2: Memory Leaks Description: Memory leaks occur when objects or resources are allocated in memory but not properly released, leading to excessive memory usage over time. In JavaScript, this can happen due to unintentional retention of references to objects or event listeners that are not properly cleaned up.

Solution: To prevent memory leaks, it’s essential to release unused resources and remove event listeners when they are no longer needed. One effective strategy is to use the removeEventListener method to detach event listeners. Here’s an example:

function handleClick() {
  console.log('Button clicked');
}

const button = document.getElementById('myButton');
button.addEventListener('click', handleClick);

// Remove event listener when it's no longer needed
button.removeEventListener('click', handleClick);

By explicitly removing the event listener using removeEventListener, we ensure that the associated resources are properly released, preventing memory leaks.

Problem 3: Cross-Origin Resource Sharing (CORS) Errors Description: CORS errors occur when a web application attempts to make a request to a different domain, and the server doesn’t allow cross-origin requests due to security restrictions. This can prevent the client-side code from accessing the requested resources.

Solution: To resolve CORS errors, the server needs to include appropriate CORS headers in its response. These headers indicate which domains are allowed to access the server’s resources. Here’s an example of setting CORS headers in an Express.js server:

const express = require('express');
const app = express();

// Enable CORS for all routes
app.use((req, res, next) => {
  res.header('Access-Control-Allow-Origin', '*');
  res.header('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE');
  res.header('Access-Control-Allow-Headers', 'Content-Type');
  next();
});

// Rest of the server code...

In the above code snippet, the server includes the necessary CORS headers to allow requests from any domain (Access-Control-Allow-Origin: '*') and specifies the allowed HTTP methods (Access-Control-Allow-Methods) and headers (Access-Control-Allow-Headers). Adjust these headers based on your specific requirements and security considerations.

By properly configuring the server’s CORS headers, the client-side code can make cross-origin requests without triggering CORS errors.