The functionality of Expo FileSystem.writeAsStringAsync does not resemble that of a Promise

Question

The functionality of Expo FileSystem.writeAsStringAsync does not resemble that of a Promise

While using the Expo.writeAsStringAsync() function, I encountered a situation where it took different times to write files of different sizes, which is expected. However, I noticed that there is no way to determine when the writing process has finished because the function does not return anything. This means that if I try to access the file immediately after writing it, it may still be in the process of being written and appear empty.

Is there any method to receive a notification or response indicating that the writing process has been completed, similar to a normal promise-then-catch pattern?

On a side note, I attempted to promisify the function but did not succeed.

javascript react-native promise expo

Answer 1

Answer №1

It has come to my attention that the API documentation can be misleading due to the lack of specified return type.

Upon further investigation, I discovered that the API call is actually defined as an async function (refer to source code):

export async function writeAsStringAsync(
  fileUri: string,
  contents: string,
  options: WritingOptions = {}
): Promise<void> {
  // ...
}

As with all async functions, it returns a Promise (as indicated in the TypeScript signature above, stating Promise<void>).

This indicates that you can either use the returned Promise and await for it, or use .then() to await the completion of the filesystem call.

await Expo.writeAsStringAsync(fileUri, contents, options);
// Perform actions once the writing is complete 
// Errors can be caught using a try/catch block

Alternatively,

Expo.writeAsStringAsync(fileUri, contents, options).then(
  () => { /* Perform actions once the writing is complete */ }
).catch(err => { /* Handle errors */ }

Answer 2

It has come to my attention that the API documentation can be misleading due to the lack of specified return type.

Upon further investigation, I discovered that the API call is actually defined as an async function (refer to source code):

export async function writeAsStringAsync(
  fileUri: string,
  contents: string,
  options: WritingOptions = {}
): Promise<void> {
  // ...
}

As with all async functions, it returns a Promise (as indicated in the TypeScript signature above, stating Promise<void>).

This indicates that you can either use the returned Promise and await for it, or use .then() to await the completion of the filesystem call.

await Expo.writeAsStringAsync(fileUri, contents, options);
// Perform actions once the writing is complete 
// Errors can be caught using a try/catch block

Alternatively,

Expo.writeAsStringAsync(fileUri, contents, options).then(
  () => { /* Perform actions once the writing is complete */ }
).catch(err => { /* Handle errors */ }

The functionality of Expo FileSystem.writeAsStringAsync does not resemble that of a Promise

Answer №1

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