Question 397594 in Javascript Question posted in
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Javascript – NodeJS Async function called once only in a loop

Following is my code structure. I have two async functions from source.js and db.js. I’m exporting these functions and calling them in test.js.

test.js calls the function async loadFromFile() to read and return a list of json data elements. For every element in the list, it then calls async writeToDB().

Expected: N number of true in console

Result: Only 1 true output in console and only one element written to the database.

// source.js
async function loadFromFile() {
    const data = await fs.readFile('/path//to/.json', { encoding: 'utf8' });
    const ret = JSON.parse(data);
    return ret;
}
exports.loadFromFile = loadFromFile;

// db.js
async function writeToDB(data){
    console.log(data.length);    // THIS shows N data elements
    const query_str = "...";
    try{
        const response = await driver.executeQuery(query_str, ...);
        if (response){
            return true;
        }
   } catch(err){
        console.log('Error in query: '+ err);
   } finally {
        await driver.close();
   }
   // something went wrong
   return false;
}
exports.writeToDB = writeToDB;

// test.js
const source = require("./source")
const db = require("./db")

source.loadFromFile()
      .then(data_list => {
           console.log(data.length);    // This shows N data elements
           for (json_data of data_list){
                db.writeToDB(json_data)
                    .then(resp => console.log(resp))
                    .catch(error => console.error(error));
           }
    })
    .catch(error => console.error(error));
Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    Thanks to @"Daniel A white", @Bergi and @"Bilal Azam". Removing driver.close and calling the functions in their separate async-await solved the issue. The final code looks as follows

    // source.js
async function loadFromFile() {
    const data = await fs.readFile('/path//to/.json', { encoding: 'utf8' });
    const ret = JSON.parse(data);
    return ret;
}
exports.loadFromFile = loadFromFile;

    // db.js
async function writeToDB(data){
    console.log(data.length);    // THIS shows N data elements
    const query_str = "...";
    try{
        const response = await driver.executeQuery(query_str, ...);
        if (response){
            return true;
        }
   } catch(err){
        console.log('Error in query: '+ err);
   }
   return false;
}
exports.writeToDB = writeToDB;

    // test.js
const source = require("./source");
const db = require("./db");

async function process() {
    const data = await source.loadFromFile();
    for (json_data of data){
        try {
            const resp = await db.writeToDB(json_data);
            if (!resp) {console.log('Error writing to DB');}
        } catch(err){console.log('Error:'+ err);};
    }
}

process()    
    .then(d => console.log(d))
    .catch(error => console.error(error));

    Log output is as expected and all the data gets written to the DB as expected. However, the running node test.js on terminal gets stuck and never exits unless done manually using ctrl-c.


  2. 0

    You are currently not awaiting the writeToDB calls inside the loop, and so time taken inside this loop isn’t going to get extended for the completion of these asyncops to finish execution.

    Here is your test.js code corrected, waiting on each writeToDB call properly:

    const source = require("./source")
const db = require("./db")

async function processFile() {
    try {
        const data_list = await source.loadFromFile();
        console.log(data_list.length);

        for (const json_data of data_list) {
            try {
                const resp = await db.writeToDB(json_data);
                console.log(resp);
            } catch (error) {
                console.error('Error writing to DB:', error);
            }
        }
    } catch (error) {
        console.error('Error loading file:', error);
    }
}

processFile();
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