FFlate zip callback not functioning!

[Umisyus]

Hi there, I'm trying to use this zip function to return my zipped files out of my function through variable assignment. The problem is, when I do that the callback does not assign my result and I receive undefined.
Here is an example in Typescript:

function processFile(left: number, file: { key: string, value: Buffer }) {
    let result: Uint8Array | undefined;

    bufToU8(file.value, (buf: Uint8Array) => {
        // With fflate, we can choose which files we want to compress
        zipObj[file.key] = [buf, {
            level: 0
        }];

        // If we didn't want to specify options:
        // zipObj[file.name] = buf;
    });
    if (!--left) {
       zip(zipObj, function (err, out) {
            if (err) { console.error(err); throw err; }

/* PROBLEM HAPPENS HERE */
            result = out
            console.log("Done zipping");

/* THIS WORKS, BUT I NEED A WAY TO RETURN FROM THE `processFile` FUNCTION */
// fs.writeFile('test.zip', out)

        });
       
    }

    return result
}

Thanks for your time.

[101arrowz]

The problem is that zip is an asynchronous function, but you want to use it in a synchronous function. Asynchronous functions can only be used with callbacks or (preferably) Promise. In other words, what you're asking is not possible; you should probably create a callback parameter for processFile to "return" your value.

Also, I'm not sure the --left bit of this code will work if you call processFile multiple times, as it doesn't actually decrement the value in the caller. left is passed by value to processFile, not as a reference.

[Umisyus]

Thanks for your quick reply. So zip is an async function, so I could do this:

const files = [
{key:'test1',value:"ABCDEFGH123"},
{key:'test2',value:"ABCDEFGH12345"},
]

const myZipOptions = {level: 0}
let myObjectWithAFileTree = {}

for (let file of files) { myObjectWithAFileTree[file.key] = [ file.value ] }

export const zipFiles = (
  data: AsyncZippable,
  options: AsyncZipOptions = { level: 0 }
): Promise<Uint8Array> => {
  return new Promise((resolve, reject) => {
    zip(data, options, (err, data) => {
      console.warn("err = ", err);
      console.log("data = ", data);
      if (err) return reject(err);
      return resolve(data);
    });
  });
};

Then I would call it like this: await zipFiles(myObjectWithAFileTree, myZipOptions)
Regarding the left parameter, I have it decremented outside of the function.

let files = [
{key:'test1',value:"ABCDEFGH123"},
{key:'test2',value:"ABCDEFGH12345"},
]

let myObjectWithAFileTree = {}
for (let file of files) { myObjectWithAFileTree[file.key] = [ file.value ] }

let zipResult = await zipFiles(myObjectWithAFileTree,myZipOptions)

fs.promises.writeFile("results.zip", zipResult)

Regarding the left parameter, I have it decremented outside of the function.

[101arrowz]

Yes, your first example is nearly correct. However, if you have strings as your values, you need to make them Uint8Array to use. Like this:

import { strToU8 } from 'fflate';
// Instead of: for (let file of files) { myObjectWithAFileTree[file.key] = [ file.value ] }
for (let file of files) { myObjectWithAFileTree[file.key] = [ strToU8(file.value) ];

[Umisyus]

So I should be good then? Thanks a lot man. My values are Buffers, which use UInt8Arrays.

Thanks a lot man.
Peace

[Umisyus]

Issue may be closed now.