CODEWITHSUNDEEP
javascriptnode.js
the thinker
the thinker

Reputation: 484

How do I make a function wait for the completion of another function before running

The problem I'm facing is that I want to create a temporary work folder for a certain function to hold its assets and work on them.

So:

await function someFunc() {
    createFolder()
    ...
    makeSomeFiles()
    doOtherStuff()
    ...
    deleteFolder()
}

But the functions that I am using, in node.js, are all async. Creating a folder is fs.mkdir() and deleting a folder is fs.rmdir() and downloading images and saving them is also an async procedure of some kind.

The problem is such: the folder gets created, and deleted, before any of the code in the middle executes. So I get errors from the middle section code that the folder doesn't exist, because it gets deleted prematurely. How do i make fs.rmdir(), at the end, wait for all the middle code to run first, before deleting the folder.

The specific code is this:

async function run() {
    //GENERATE SESSION ID AND FOLDER
    const sessionID = str.random(50);
    fs.mkdir('images/'+sessionID, (err) => {
        if (err) return err;
    });

    //DOWNLOAD IMAGE
    https.get('https://en.wikipedia.org/wiki/Main_Page#/media/File:RE_Kaja_Kallas.jpg', (file) => {
        file.pipe(fs.createWriteStream('images/'+sessionID+'/image.jpeg'));
    });


    //CLEANUP
    fs.rmdir('images/'+sessionID, { recursive: true }, (err) => {
        if (err) return err;
    });
}

Upvotes: 0

Views: 379

Answers (1)

jfriend00
jfriend00

Reputation: 708056

I would use promise-based versions of functions that do these operations and then use async/await with those promises:

const stream = require('stream');
const {promisify} = require('util');
const fs = require('fs');
const fsp = fs.promises;
const got = require('got');

const pipeline = promisify(stream.pipeline);

async function run() {
     const sessionID = str.random(50);
     const dir = 'images/'+sessionID;
     await fsp.mkdir(dir);

     await pipeline(
         got.stream('https://en.wikipedia.org/wiki/Main_Page#/media/File:RE_Kaja_Kallas.jpg'),
         fs.createWriteStream(dir + '/image.jpeg')
     );

     // not sure why you're trying to remove a directory that you just 
     // put a file in so it's not empty
     await fsp.rmdir(dir, { recursive: true })
}

run().then(() => {
    console.log("all done");
}).catch(err => {
    console.log(err);
});

But, this function isn't making a lot of sense to me because you're creating a directory, downloading a file to it and then trying to remove a non-empty directory.

This uses the library got() for downloading the file because it's my goto library for http requests since it has both stream and promise interfaces.

Upvotes: 2

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