fs.readFile() returns undefined [duplicate] - html

Question

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Returning a value from callback function in Node.js [duplicate]
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How do I return the response from an asynchronous call?
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Closed 2 years ago.
i'm trying to display a html page creating a node http server, when i try to take the code of the html file it returns undefined, this is the code...
var http = require('http');
var fileContent = function(path, format) {
var fs = require('fs');
fs.readFile(path, format, function(error, contents) {
if (error) throw error;
return contents;
});
}
var server = http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/html'});
page = fileContent('./page.html','utf8');
console.log(page);
res.end(page);
}).listen(8080);
i printed the error,
[Error: ENOENT: no such file or directory, open './page.html'] {
errno: -2,
code: 'ENOENT',
syscall: 'open',
path: './page.html'
}
the two files are in the same directory

Answer 1

Firstly, fs.readFile is asynchronous function. Which means is not returning the answer instantly or blocks the thread to wait for answer. Instead it requires a callback to let you know when answer is ready.
Secondly, I suggest using path module to merge __dirname (the directory name of the current module) and file name to make absolute file paths.
I will provide 3 solutions using different methods.
Solution 1. Using callback method
var http = require('http');
var fs = require('fs');
var path = require('path');
var fileContent = function(path, format, cb) {
fs.readFile(path, format, function(error, contents) {
if (error) throw error;
cb(contents);
});
}
var server = http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/html'});
fileContent(path.join(__dirname, 'page.html'), 'utf8', function (page) {
console.log(page);
res.end(page);
});
}).listen(8080);
Solution 2. Promises using .then
var http = require('http');
var fs = require('fs');
var path = require('path');
var fileContent = function(path, format) {
return new Promise(function (resolve, reject) {
fs.readFile(path, format, function(error, contents) {
if (error) reject(error);
else resolve(contents);
});
});
}
var server = http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/html'});
fileContent(path.join(__dirname, 'page.html'), 'utf8')
.then(function(page) {
console.log(page);
res.end(page);
});
}).listen(8080);
Solution 3. Promise using async/await
var http = require('http');
var fs = require('fs');
var path = require('path');
var fileContent = function(path, format) {
return new Promise(function (resolve, reject) {
fs.readFile(path, format, function(error, contents) {
if (error) reject(error);
else resolve(contents);
});
});
}
var server = http.createServer(async function (req, res) {
res.writeHead(200, {'Content-Type': 'text/html'});
var page = await fileContent(path.join(__dirname, 'page.html'), 'utf8');
console.log(page);
res.end(page);
}).listen(8080);