Handling multiple error cases in promise chains

26 Oct 2023

promises

When working with promises in JavaScript, it’s common to chain multiple asynchronous operations together using .then() and .catch() methods. However, when dealing with complex scenarios involving multiple error cases, it can be a challenge to handle each case correctly.

Fortunately, JavaScript provides various techniques to handle multiple error cases in promise chains effectively. Let’s explore some approaches:

Using multiple `.catch()` blocks

One way to handle multiple error cases is by using multiple .catch() blocks in the promise chain. Each .catch() block can handle a specific type of error or specific error condition. Here’s an example:

promise
  .then((result) => {
    // handle success case
  })
  .catch((error) => {
    // handle first error case
  })
  .catch((error) => {
    // handle second error case
  })
  .catch((error) => {
    // handle remaining error cases
  });

In this approach, the promise chain will execute the appropriate .catch() block based on the error type or condition that occurred. The subsequent .catch() blocks will skip if a preceding block has handled the error.

Using `Promise.reject()` with conditional logic

Another approach to handle multiple error cases is by using Promise.reject(). By conditionally rejecting the promise, you can guide the flow to a specific .catch() block. Here’s an example:

promise
  .then((result) => {
    if (/* condition for specific error case */) {
      return Promise.reject(new Error('Specific Error'));
    }
    // continue normal execution
  })
  .catch((error) => {
    if (error.message === 'Specific Error') {
      // handle specific error case
    } else {
      // handle remaining error cases
    }
  });

In this approach, when a specific error condition is met, Promise.reject() is called with a custom error object. The subsequent .catch() block can then check the error message to determine which error case to handle.

Using `async/await` with `try/catch`

If you’re using async/await syntax in your codebase, handling multiple error cases becomes simpler and more readable using try/catch blocks. Here’s an example:

try {
  const result = await promise;
  // handle success case
} catch (error) {
  // handle multiple error cases
  if (/* condition for specific error case */) {
    // handle specific error case
  } else {
    // handle remaining error cases
  }
}

In this approach, the promise is awaited within a try block, and any errors are caught in the catch block. You can then use conditional logic to handle specific error cases.

Conclusion

Handling multiple error cases in promise chains can be challenging, but with the right techniques, it becomes more manageable. By using multiple .catch() blocks, Promise.reject() with conditional logic, or async/await with try/catch, you can effectively handle different error scenarios and ensure your code is robust.

Remember, it’s important to consider the specific requirements of your application and choose the approach that best fits your use case.

#javascript #promises

Using multiple .catch() blocks

Using Promise.reject() with conditional logic

Using async/await with try/catch

Conclusion

Using multiple `.catch()` blocks

Using `Promise.reject()` with conditional logic

Using `async/await` with `try/catch`