function is being executed twice when called only once

Question

I am making a program that will read content of files inside nested folders.For now I am just trying to log the content of the file in console. But I am getting two logs instead of only one.Here is what I have done till now

const fs = require('fs');
const path = require('path');
const { promisify } = require('util');
const getStats = promisify(fs.stat);
const readdir = promisify(fs.readdir);
const http = require('http');

handle_files = async (req, res) => {
    let files = await scanDir("logs_of_109");
    let result = await read_content(files)
    check_file_content(result)
    res.writeHead(200, { 'Content-Type': 'text/html' });
    // console.log(result)
    res.write("Hello");
    res.end();
};

check_file_content = (file_data) => {
    console.log(file_data[1])
}

async function read_content(files) {
    let file_data = []
    files.map(file => {
        let start_index = file.toString().lastIndexOf('.') + 1
        let ext = file.substring(start_index, file.length)
        if (ext == 'data') {
            file_data.push(fs.readFileSync(file, { encoding: 'utf-8' }))
        }
    })
    return file_data
}

http.createServer(handle_files).listen(8080)

async function scanDir(dir, fileList = []) {
    // fetch list of files from the giver directory
    let files = await readdir(dir);
    // loop through all the files
    for (let file of files) {
        // join new folder name after the parent folder
        // logs_of_109/24
        let filePath = path.join(dir, file);
        try {
            // 
            let stats = await getStats(filePath);
            if (!stats.isDirectory()) {
                // add the filepath to the array
                fileList.push(filePath);
            }
            if (stats.isDirectory()) {
                await scanDir(filePath, fileList);
            }
        } catch (err) {
            // Drop on the floor.. 
        }
    }

    return fileList;
}

I expect the file content to be logged only once but it is logging twice on my console. Why is this happening and how do I stop this?

Answer 1

The answer above is correct. My approach is to solve it via 'routing' of any kind. Here is small basic example of how it can be done

const fs = require('fs');
const path = require('path');
const { promisify } = require('util');
const getStats = promisify(fs.stat);
const readdir = promisify(fs.readdir);
const http = require('http');

handle_routes = async (req, res) => {
    switch(req.url) {
        case '/files':
            handle_files(req, res);
        default:
            console.log('for default page');
    }
}

handle_files = async (req, res) => {
    let files = await scanDir("logs_of_109");
    let result = await read_content(files)
    check_file_content(result)
    res.writeHead(200, { 'Content-Type': 'text/html' });
    res.write("Hello");
    res.end();
};

check_file_content = (file_data) => {
    console.log(file_data[1])
}

async function read_content(files) {
    let file_data = []
    files.map(file => {
        let start_index = file.toString().lastIndexOf('.') + 1
        let ext = file.substring(start_index, file.length)
        if (ext == 'data') {
            file_data.push(fs.readFileSync(file, { encoding: 'utf-8' }))
        }
    })
    return file_data
}

http.createServer(handle_routes).listen(8080)

async function scanDir(dir, fileList = []) {
    // fetch list of files from the giver directory
    let files = await readdir(dir);
    // loop through all the files
    for (let file of files) {
        // join new folder name after the parent folder
        // logs_of_109/24
        let filePath = path.join(dir, file);
        try {
            // 
            let stats = await getStats(filePath);
            if (!stats.isDirectory()) {
                // add the filepath to the array
                fileList.push(filePath);
            }
            if (stats.isDirectory()) {
                await scanDir(filePath, fileList);
            }
        } catch (err) {
            // Drop on the floor.. 
        }
    }

    return fileList;
}

This gives you possibility to call handle_files function by going to localhost:8080/files url

Answer 2

Your browser is making two requests to your server, most likely one for the URL you put in the address bar and another for favicon.ico. (You can quickly tell by opening the dev tools on your browser and going to the Network tab.)

handleFiles should look at req (specifically its url property) and act according to what's being requested. (This is something the code should be doing anyway.)

---

Side note 1: You're passing an async function into something (createServer) that won't do anything with the promise it returns. If you do that, it's important to catch any errors in the function locally within the function, since (again) nothing else is going to handle them. E.g.:

handle_files = async (req, res) => {
    try {
        let files = await scanDir("logs_of_109");
        let result = await read_content(files)
        check_file_content(result)
        res.writeHead(200, { 'Content-Type': 'text/html' });
        // console.log(result)
        res.write("Hello");
        res.end();
    } catch (e) {
        // ...handle error here...
    }
};

Side note 2: That code is falling prey to The Horror of Implicit Globals¹. Declare your variables in the appropriate scope. Not declaring them, in loose mode, makes them globals. (Also recommend using strict mode, so you get an error for this.)

---

¹ (that's a post on my anemic little blog)