I am doing some experimentation with Node.js and would like to read a JSON object, either from a text file or a .js file (which is better??) into memory so that I can access that object quickly from code. I realize that there are things like Mongo, Alfred, etc out there, but that is not what I need right now.
How do I read a JSON object out of a text or js file and into server memory using JavaScript/Node?
This question is related to
javascript
json
node.js
In Node 8 you can use the built-in util.promisify()
to asynchronously read a file like this
const {promisify} = require('util')
const fs = require('fs')
const readFileAsync = promisify(fs.readFile)
readFileAsync(`${__dirname}/my.json`, {encoding: 'utf8'})
.then(contents => {
const obj = JSON.parse(contents)
console.log(obj)
})
.catch(error => {
throw error
})
If you are looking for a complete solution for Async
loading a JSON file from Relative Path
with Error Handling
// Global variables
// Request path module for relative path
const path = require('path')
// Request File System Module
var fs = require('fs');
// GET request for the /list_user page.
router.get('/listUsers', function (req, res) {
console.log("Got a GET request for list of users");
// Create a relative path URL
let reqPath = path.join(__dirname, '../mock/users.json');
//Read JSON from relative path of this file
fs.readFile(reqPath , 'utf8', function (err, data) {
//Handle Error
if(!err) {
//Handle Success
console.log("Success"+data);
// Parse Data to JSON OR
var jsonObj = JSON.parse(data)
//Send back as Response
res.end( data );
}else {
//Handle Error
res.end("Error: "+err )
}
});
})
Directory Structure:
using node-fs-extra (async await)
const readJsonFile = async () => {
try {
const myJsonObject = await fs.readJson('./my_json_file.json');
console.log(myJsonObject);
} catch (err) {
console.error(err)
}
}
readJsonFile() // prints your json object
https://nodejs.org/dist/latest-v6.x/docs/api/fs.html#fs_fs_readfile_file_options_callback
var fs = require('fs');
fs.readFile('/etc/passwd', (err, data) => {
if (err) throw err;
console.log(data);
});
// options
fs.readFile('/etc/passwd', 'utf8', callback);
https://nodejs.org/dist/latest-v6.x/docs/api/fs.html#fs_fs_readfilesync_file_options
You can find all usage of Node.js at the File System docs!
hope this help for you!
Using fs-extra package is quite simple:
Sync:
const fs = require('fs-extra')
const packageObj = fs.readJsonSync('./package.json')
console.log(packageObj.version)
Async:
const fs = require('fs-extra')
const packageObj = await fs.readJson('./package.json')
console.log(packageObj.version)
The easiest way I have found to do this is to just use require
and the path to your JSON file.
For example, suppose you have the following JSON file.
test.json
{
"firstName": "Joe",
"lastName": "Smith"
}
You can then easily load this in your node.js application using require
var config = require('./test.json');
console.log(config.firstName + ' ' + config.lastName);
At least in Node v8.9.1, you can just do
var json_data = require('/path/to/local/file.json');
and access all the elements of the JSON object.
function parseIt(){
return new Promise(function(res){
try{
var fs = require('fs');
const dirPath = 'K:\\merge-xml-junit\\xml-results\\master.json';
fs.readFile(dirPath,'utf8',function(err,data){
if(err) throw err;
res(data);
})}
catch(err){
res(err);
}
});
}
async function test(){
jsonData = await parseIt();
var parsedJSON = JSON.parse(jsonData);
var testSuite = parsedJSON['testsuites']['testsuite'];
console.log(testSuite);
}
test();
So many answers, and no one ever made a benchmark to compare sync vs async vs require. I described the difference in use cases of reading json in memory via require, readFileSync and readFile here.
Asynchronous is there for a reason! Throws stone at @mihai
Otherwise, here is the code he used with the asynchronous version:
// Declare variables
var fs = require('fs'),
obj
// Read the file and send to the callback
fs.readFile('path/to/file', handleFile)
// Write the callback function
function handleFile(err, data) {
if (err) throw err
obj = JSON.parse(data)
// You can now play with your datas
}
Source: Stackoverflow.com