How to detect if browser support specified css pseudo-class?

You can simply check if your style with pseudo-class was applied.

Something like this: http://jsfiddle.net/qPmT2/1/

stylesheet.insertRule(rule, index) method will throw error if the rule is invalid. so we can use it.

var support_pseudo = function (){
    var ss = document.styleSheets[0];
    if(!ss){
        var el = document.createElement('style');
        document.head.appendChild(el);
        ss = document.styleSheets[0];
        document.head.removeChild(el);
    }
    return function (pseudo_class){
        try{
            if(!(/^:/).test(pseudo_class)){
                pseudo_class = ':'+pseudo_class;
            }
            ss.insertRule('html'+pseudo_class+'{}',0);
            ss.deleteRule(0);
            return true;
        }catch(e){
            return false;
        }
    };
}();


//test
support_pseudo(':hover'); //true
support_pseudo(':before'); //true
support_pseudo(':hello'); //false
support_pseudo(':world'); //false