When and Why Should We Combine async/await with .then() in JavaScript?

Combining Async/Await and .then() with Promise Conversions

In JavaScript, async/await is a powerful mechanism for handling asynchronous operations. However, there are situations where it may be convenient to combine async/await with .then(), especially when converting Promises into async functions.

Consider the following example:

<code class="javascript">async apiCall(params) {
    var results = await this.anotherCall()
      .then(results => {
        //do any results transformations
        return results;
      })
      .catch(error => {
        //handle any errors here
      });
    return results;
  }</code>

Here, the anotherCall() method returns a Promise, which is converted into an async function using .then().catch(). This allows us to perform any necessary transformations or error handling before returning the results.

Some developers prefer using async/await with .catch() instead of try/catch for its compactness. For instance:

<code class="javascript">async function asyncTask() {
  throw new Error('network')
}
async function main() {
  const result = await asyncTask().catch(error => console.error(error));
  console.log('result:', result)
}

main();</code>

In this example, the asyncTask() function throws an error, which is caught by the .catch() method within the await call. This prevents the error from propagating and allows us to handle it gracefully within the main() function.

It's important to note that the .then() method creates and returns a new Promise, even if the original Promise returned by anotherCall() already resolved. This behavior can lead to unexpected side effects, especially if multiple Promises are chained together using .then().

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