downloadTopic.js

function exportToCsv(filename, rows) {
	var processRow = function (row) {
		var finalVal = '';
		for (var j = 0; j < row.length; j++) {
			var innerValue = row[j] === null ? '' : row[j].toString();
			if (row[j] instanceof Date) {
				innerValue = row[j].toLocaleString();
			};
			var result = innerValue.replace(/"/g, '""');
			if (result.search(/("|,|\n)/g) >= 0)
				result = '"' + result + '"';
			if (j > 0)
				finalVal += ',';
			finalVal += result;
		}
		return finalVal + '\n';
	};

	var csvFile = '';
	for (var i = 0; i < rows.length; i++) {
		csvFile += processRow(rows[i]);
	}

	var blob = new Blob([csvFile], { type: 'text/csv;charset=utf-8;' });
	if (navigator.msSaveBlob) { // IE 10+
		navigator.msSaveBlob(blob, filename);
	} else {
		var link = document.createElement("a");
		if (link.download !== undefined) { // feature detection
			// Browsers that support HTML5 download attribute
			var url = URL.createObjectURL(blob);
			link.setAttribute("href", url);
			link.setAttribute("download", filename);
			link.style.visibility = 'hidden';
			document.body.appendChild(link);
			link.click();
			document.body.removeChild(link);
		}
	}
}

function emit(method, data) {
	return new Promise((resolve, reject) => {
		window.socket.emit(method, data, (err, result) => {
			
			if (err) {
				reject(err);
			} else {
				setTimeout(() => resolve(result), 1000);
			}
		});
	});
}
function getAllPosts(topicId) {
	return new Promise((resolve, reject) => {
		let idx = 0, result = [];
		const iterate = () => emit('topics.loadMore', {
			tid: topicId,
			after: idx,
			direction: 1
		}).then((results) => {
			if (!results.posts || !results.posts.length) {
				return resolve(result);
			}
			idx += results.posts.length;
			result = result.concat(results.posts)
			return Promise.resolve().then(iterate).catch(reject);
		}).catch((err) => reject(err));
		iterate();
	});
}

function downloadTopic(topicId) {
	return getAllPosts(topicId).then(posts => {
		let rows = [['pid','uid','username','timestamp','content']];
		posts.forEach(post=>{
			rows.push([post.pid,post.uid,post.user.username,post.timestampISO,post.content]);
		});
		exportToCsv(`${topicId}.csv`, rows);
		return rows;
	});
}

downloadTopic(20937).then(result=>console.log(result))