How can I return the value from an async function in React Native ? I am trying to compress images which was given by user.
Here is my compress function where compress each image
const compressFunction = async (item, format = SaveFormat.JPEG) => {
const result = await manipulateAsync(
item.uri,
[],
{ compress: 0, format }
)
return result
};
Here is the function I try to call it. This is not working, console.log return Promise { _u 0, _v 0, _w null, _x null }. compressFunction is working and i can console.log and see the result for each return of "compressFunction(item)" but i can't see them in array list.
const compressImages = (items) => {
const list = items.map( async (item) => ( await compressFunction(item)) )
console.log(list)
}
But for example when i try to call like that it is working.
const compressImages = async (items) => {
const list= await compressFunction(items[0])
console.log(list)
}
I couldn't catch what im doing wrong, I'm working on it for hours. If someone can help me I would be grateful
CodePudding user response:
try await Promise.all(items.map(compressFunction))
Calling list.map(async function)
will transform each element in list into a Promise.
Edit: if you make this much more verbose you can see what's going on here
const promises = items.map(item => {
return new Promise((res) => {
compressFunction(item).then(result => {
return res(result);
});
});
});
// Now with the list of promises we have to use the Promise api
// to wait for them all to finish.
Promise.all(promises).then(results => {
// do stuff with results
});
Async/await is just shorthand for this syntax