slim.js

/* naive version of the css plugin for the slim loader */
module.exports = function(moduleId, config) {
	return new CssModule(config.paths[config.bundles[moduleId]]).injectLink();
};

function CssModule(address) {
	this.address = address;
}

// timeout in seconds
CssModule.waitTimeout = 60;

// The slim build does not resolve to URLs, so this trick is needed
// to get the url and use it to check if the link was already added
// to the head
CssModule.prototype.getLinkUrl = function() {
	var anchor = document.createElement("a");
	anchor.href = this.address;
	return anchor.href;
};

CssModule.prototype.linkExists = function() {
	var styleSheets = document.querySelectorAll('[rel="stylesheet"]');

	if (styleSheets != null) {
		var href = this.getLinkUrl();
		for (var i = 0; i < styleSheets.length; ++i) {
			if (href === styleSheets[i].href) {
				return true;
			}
		}
	}

	return false;
};

CssModule.prototype.injectLink = function() {
	if (this._loadPromise) {
		return this._loadPromise;
	}

	if (this.linkExists()) {
		this._loadPromise = Promise.resolve("");
		return this._loadPromise;
	}

	// inspired by https://github.com/filamentgroup/loadCSS
	var link = (this.link = document.createElement("link"));
	link.type = "text/css";
	link.rel = "stylesheet";
	link.href = this.address;

	// wait until the css file is loaded
	this._loadPromise = new Promise(function(resolve, reject) {
		var timeout = setTimeout(function() {
			reject("Unable to load CSS");
		}, CssModule.waitTimeout * 1000);

		var linkEventCallback = function(event) {
			clearTimeout(timeout);

			link.removeEventListener("load", linkEventCallback);
			link.removeEventListener("error", linkEventCallback);

			if (event && event.type === "error") {
				reject("Unable to load CSS");
			} else {
				resolve("");
			}
		};

		link.addEventListener("load", linkEventCallback);
		link.addEventListener("error", linkEventCallback);

		document.head.appendChild(link);
	});

	return this._loadPromise;
};