How to detect if an external library has loaded

detect_library.js

	window.create_widget = function() {

		if (jQuery("#box-dynamic").length)
			$('#box-dynamic').html("Oh Yes");

	}

	window.loadjQuery = function(url, success) {

		var script = document.createElement('script');
		script.src = url;
		var head = document.getElementsByTagName('head')[0],
		done = false;
		head.appendChild(script);

		// Attach handlers for all browsers
		script.onload = script.onreadystatechange = function() {

			if (!done && (!this.readyState || this.readyState == 'loaded' || this.readyState == 'complete')) {

				done = true;
				success();
				script.onload = script.onreadystatechange = null;
				head.removeChild(script);

			}

		};

	}

	if (typeof jQuery == 'undefined') {

		loadjQuery('http://code.jquery.com/jquery-2.1.1.min.js', function() {
			create_widget();
		});

	} else {
		create_widget();
	}