How to write an asynchronous program with nodejs? - node.js

Question

Lets say, for example, I want to write a nodejs program where I have two or three independent parts like fs.readdir, fs.copy, etc. on different locations, but the result all three actions is to be sent to a json file like this:
var fs = require('fs-extra');
var jsd = {
"act1" : false,
"act2" : false,
"act3" : false
}
fs.readdir(path1, function (err, files) {
if (err) jsd.act1 = err;
for (x in files) console.log(files[x]);
jsd.act1 = true;
});
fs.copy(path2, path3, function (err) {
if (err) jsd.act2 = err;
jsd.act2 = true;
});
fs.remove(path4, function (err) {
if (err) jsd.act3 = err;
jsd.act3 = true;
});
// all three of the above actions are independent, so it makes sense that all of them are executed asynchronously.
// Now we write jsd object to a json file; jsd's contents are dependent on the above actions though
fs.writeJson("./data.json", jsd, function (err, files) {
if (err) return console.error(err);
});
How do I make sure that the correct data is entered into the file data.json, i.e fs.writeJson executes after the actions previous to it are executed first?
I know one way is to nest all of them, i.e,
readdir() {
copy() {
remove() {
writeJson();
}
}
}
But this may result in callback hell, so is there a better way to do this?

Answer 1

you can use Promise or module async,
if you use promise, first you must convert all callback function into Promise like this:
const reddir = function(path) {
return new Promise((resolve, reject) => {
fs.readdir(path, (err, files) => {
if (err) return reject(err);
for (x in files) console.log(files[x]);
resolve(true);
});
})
}
then you can use
Promise.all([reddir(path1), copy(path2, path3), remove(path4)])
.spread((act1, act2, act3) => { //.spread is bluebird feature
return writeJson(./data.json);
})
.catch(e => {
// all error can handled in this
})
if you use async module, you can write like this:
async.parallel({
act1: function(cb){
fs.reddir(path1, (err, files) => {
if (err) return cb(err);
for (x in files) console.log(files[x]);
cb(true);
})
},
act2: ...
},(err, jsd) => { // jsd will be {act1: true, act2: ...}
if (err) return console.error(err); // handle all above error here;
fs.writeJson("./data.json", jsd, function (err, files) {
if (err) return console.error(err);
});
})