lazy-vimeo

<a class="vimeo-lazy-link" data-height="349" data-width="620" data-video="3137949" href="http://vimeo.com/3137949"></a>

function fetchJSONFile(path, callback) {
    var httpRequest = new XMLHttpRequest();
    httpRequest.onreadystatechange = function() {
        if (httpRequest.readyState === 4) {
            if (httpRequest.status === 200) {
                var data = JSON.parse(httpRequest.responseText);
                if (callback) callback(data);
            }
        }
    };
    httpRequest.open('GET', path);
    httpRequest.send(); 
}

(function() {
  // Find all Vimeo videos
	var lazy_links = document.querySelectorAll('.vimeo-lazy-link')
	  , vimeo_id;

	for (var i = 0; i < lazy_links.length; i++) {
	  vimeo_id = lazy_links[i].getAttribute('data-video');

    fetchJSONFile('http://vimeo.com/api/v2/video/' + vimeo_id + '.json?callback=?', function(response){
      lazy_links[i].setAttribute('style', 'background: url(' + response[0].thumbnail_medium + '); background-size: cover; width: 600px; height: 350px;');
    });
	}
})();