Nested JavaScript Loops Containing Async Functions That are Forced to Run Synchronously

translate.js

var translate = require('google-translate-api');
var fs = require('fs');
var async = require('async');

// array of filenames
// each file contains a JSON object
var filenames = [
"0001-school-life-buying-textbooks.js",
"0002-school-life-class-registration.js",
"0003-school-life-too-many-full-classes.js"
]

// loop over each filename and process asynchronously
async.eachSeries(filenames, function(filename, callback) {
	// read each file synchronously and parse it into an object
	var obj = JSON.parse(fs.readFileSync('dialogues/'+filename, 'utf8'));
	var array1 = [];

	// loop over each sentence and process asynchronously
	async.eachSeries(obj.sentences, function(sentence, callback) {
		// create an object to store the English and Indonesian sentence, e.g.
		/*{
			"English": "How are you",
			"Indonesian": "Apa kabar"
		}*/
		var translatedSentence = {};
		translatedSentence["English"] = sentence.English;

		// call translate function to translate English sentence into Indonesian
		// even though translate function is async, this loop will run synchronously
		translate(sentence.English, {from: 'en', to: 'id'}).then(res => {
			translatedSentence["Indonesian"] = res.text;
			array1.push(translatedSentence);
			callback();
		}).catch(err => {
			console.error(err);
			callback();
		});
	}, function(err) {
		// if any of the file processing produced an error, err would equal that error
		if( err ) {
			// One of the iterations produced an error.
			// All processing will now stop.
			console.log('A sentence failed to process');
		} else {
			// write the array of translated sentence objects to file synchronously
			var stream = fs.createWriteStream("indonesian/"+filename);
			stream.once('open', function(fd) {
				stream.write(JSON.stringify(array1, null, '\t')+"\n");
				stream.end();
			});
			console.log('All sentences have been processed successfully');
		}
	});
	callback();
}, function(err) {
	if( err ) {
		// One of the iterations produced an error.
		// All processing will now stop.
		console.log('A sentence failed to process');
	} else {
		console.log('All sentences have been processed successfully');
	}
});