Get Data from Fs.Readfile

Get data from fs.readFile

To elaborate on what @Raynos said, the function you have defined is an asynchronous callback. It doesn't execute right away, rather it executes when the file loading has completed. When you call readFile, control is returned immediately and the next line of code is executed. So when you call console.log, your callback has not yet been invoked, and this content has not yet been set. Welcome to asynchronous programming.

Example approaches

const fs = require('fs');
// First I want to read the file
fs.readFile('./Index.html', function read(err, data) {
    if (err) {
        throw err;
    }
    const content = data;

    // Invoke the next step here however you like
    console.log(content);   // Put all of the code here (not the best solution)
    processFile(content);   // Or put the next step in a function and invoke it
});

function processFile(content) {
    console.log(content);
}

Or better yet, as Raynos example shows, wrap your call in a function and pass in your own callbacks. (Apparently this is better practice) I think getting into the habit of wrapping your async calls in function that takes a callback will save you a lot of trouble and messy code.

function doSomething (callback) {
    // any async callback invokes callback with response
}

doSomething (function doSomethingAfter(err, result) {
    // process the async result
});

how to get the data from fs.readfile callback function

callbacks functions means what do you want to do when data comes?

which means node will start read file and implement next line, without waiting data to came before implement your console.log.

You can make it as a function that returns promise like:

const fs = require('fs');

function getInput() {
    return new Promise((resolve, reject) => {
        let input = [];
        fs.readFile('input.txt',(err,data)=>{
            if(err) return reject(err);
            var input = data.toString().split(' ');
            return resolve(input);
        })
    });
}

getInput().then(input => console.log(input));

or, you can use async and await to wait input, read more about async.

Fs.readFile return undefined

Try the following:

const accounts = () => fs.readFileSync(__dirname + '/accounts.json', { endoding: 'utf8'})
const accRead = JSON.parse(accounts())
/*Logging for visualization*/console.log(accRead)

How to get data from fs.readFile in vuejs3

The only way to make this data available in your Vue app is to use the define plugin in Webpack:

// vue.config.js
const my_data = require('./path/file.json');
module.exports =
{
  chainWebpack: config =>
  {
    config.plugin('define').tap(args =>
    {
      args[0]['process.env'].MY_JSON_DATA = JSON.stringify(my_data);
      return args;
    });
  }
}

Then you can access your data as process.env.MY_JSON_DATA

Using fs read file I want to the json data in variable to pass to the nodejs

You try this

const {readFile} = require('fs/promises'); // using fs-promises
const path = require('path');
const file = path.join("/users/", "hello.json");
const dataObj = {}; // object you intend to use

readFile(file, {encoding: 'utf-8'}).then((result) => {

if(!dataObj[result]) {
  dataObj[result] = JSON.parse(result);
  }
});

console.log(dataObj) // result

The JSON file is read first, the result gotten from the readFile function is appended to the dataObj object. Hope it can help you or steer you in the right direction

Return value from externally called fs.Readfile() in node

You're using await and async in sendEmail but not returning any Promise (So the sendEmail function doesn't return anything and this is why you get undefined).
Nevertheless, on the response you're trying to call .then() even though you used await.

So you should:

1. return Promise in the sendEmail function.
2. decide how you want to handle it, if you use async-await then dont use .then() and just analyze the variable and vice versa.
3. generateEmail() function should also return Promise.

For example:

async function sendEmail() {
return new Promise((resolve, reject) => {
    // Check if user exists
    fs.readFile('./file.json', (err, data) => {
        if(err) {
            reject()
        }
        else {
            let users = JSON.parse(data)
            let dataToWrite = JSON.stringify(users)

            fs.writeFile('./file2.json', dataToWrite, (err) => {
                if(err) {
                    console.error(err)
                    reject()
                }
                else {
                    generateEmail(users)
                        .then((info) => {
                            resolve(info)
                        })
                        .catch(
                            console.log('err')
                            reject()
                        )
                }
            })
        }
    })
})
}

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