async/await with postgres question and nodejs questions

Question

Hi so I have this piece of code that I want to run in order, however I always end up running the last line first and then the first one. Some guidance with this would be great.

    await fs.readFile(file, "UTF-8", (err, lines) => {
        lines = lines.split(/\r?\n/);
        lines.forEach( (line) => {
                line = line.split('\t');
                let book = new Book(line[0], line[1], line[2], line[3], 
                    line[4],line[5],line[6],line[7],line[8],line[9],
                    line[10],line[11]);
                console.log(book);
            }
        );
    });
    await pgdb.closeDatabase();

Close database looks like this

    closeDatabase = async() => {
        console.log("Closed")
        this.client.end();
    }

Thanks!

Abraham Labkovsky · Accepted Answer · 2022-03-28 19:42:46Z

1

You are mixing callbacks and async/await

with callbacks, only the code inside the callback will execute after the file is retrieved. The control flow will immediately jump to the next line.

You are not awaiting anything.

try:

import fs from "fs/promises" //or require() 
// code...

const file = await fs.readFile(file, "UTF-8")

// do something with file contents

// do some more sync or async tasks

await pgdb.closeDatabase();

answered Mar 28, 2022 at 19:42

Abraham Labkovsky

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2 Comments

pikachungg Over a year ago

What would I do if I want to use a async function with file? So instead of readFile I'm now using readFileSync and then split the result and for each result I try to run an async function but it's not working. Do you have any clue on how I could approach this?

Abraham Labkovsky Over a year ago

Don't use readFileSync. Use readFile. Just make sure you are importing fs/promises instead of plain fs. That way, you use NO callbacks. You simply assign the value you await into a variable. This pauses the control flow until the filesystem call returns. As long as nothing is taking place in a callback, you are free to loop through the results of your call, (await) retrieving more data etc. If you are calling an async function and passing in file data, make sure the async function is returning a value. Simply await the function call.

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