The URL of node link
1. In edit mode (setting.edit.enable = true) , this feature fails. If you must use a similar feature, please use the 'onClick' callback for their own control.
2. If you use the 'onClick' callback function to control opening URL , then set the URL in the other custom attribute, do not use the 'url' attribute.
Default: undefined
As same as <a> tag's 'href' attribute.
var nodes = [
{ "id":1, "name":"Google CN", "url":"http://g.cn"},
......
]