можно и сплитом разбить.. какбэ:
var str = 'background-image: url([url]http://mysite.ru:8080/img/environment/circle_portret2.jpg);[/url] position: absolute; top: 73px; left: 93px; background-position: 0px 0px; background-repeat: initial initial';
var p=str.split(';');
p.forEach(function (val){console.log(val.split(':'));})