Google Apps Script to post new xkcd comics to a Slack channel

xkcdSlackBot.gs

function postUpdatedxkcdIfNecessary() {
	var properties = PropertiesService.getUserProperties();
	
	var latestComic = JSON.parse(UrlFetchApp.fetch("http://xkcd.com/info.0.json").getContentText());
	
	if (latestComic["num"] > properties.getProperty("lastComic")) {
		var title = latestComic["title"];
		var imageURL = latestComic["img"];
		var altText = latestComic["alt"];
		var number = latestComic["num"];
		var day = latestComic["day"];
		var month = latestComic["month"];
		var year = latestComic["year"];
		
		var message = {
			"token": "[SLACK AUTHENTICATION TOKEN]",
			"channel": "#xkcd",
			"text": "New xkcd!",
			"username": "xkcd bot",
			"icon_url": "[AVATAR URL]",
			"attachments": JSON.stringify([
			{
				"title": title,
				"image_url": imageURL,
			},
			{
				"fields": [
				{
					"title": "Alt text:",
					"value": altText,
					"short": false,
				},
				{
					"title": "Number",
					"value": number.toFixed(0),
					"short": true,
				},
				{
					"title": "Date Posted",
					"value": month + "/" + day + "/" + year,
					"short": true,
				},
				{
					"title": "This comic on explain xkcd:",
					"value": "http://www.explainxkcd.com/wiki/index.php/" + number.toFixed(0),
					"short": false,
				}
				],
			},
			]),
		};
		
		var options = {
			"method": "post",
			"payload": message,
		};
		var response = JSON.parse(UrlFetchApp.fetch("https://slack.com/api/chat.postMessage", options).getContentText());
		
		// Set that there was a new latest comic only if there wasn't any errors
		// (i.e. so that we try again next time)
		if (response["ok"]) {
			properties.setProperty("lastComic", number);
		} else {
			Logger.log(response);
		}
	}
}