How to check if a class exists in CSS with jQuery

Question

I have class .hello in css:

<style>
    .hello { color:#ccc }
</style>

How can use Jquery to check class .hello exist in style or not?
Of course, it need to check all style even in <link href='style.css' /> document.

Answer 1

See below code snippet, the function returns the found class or id from the stylesheet or from style tag we pass. And returns an empty string if not found.

<script type="text/javascript">
function getDefinedCss(s){
    if(!document.styleSheets) return '';
    if(typeof s== 'string') s= RegExp('\\b'+s+'\\b','i'); // IE 
capitalizes html selectors

    var A, S, DS= document.styleSheets, n= DS.length, SA= [];
    while(n){
        S= DS[--n];
        A= (S.rules)? S.rules: S.cssRules;
            for(var i= 0, L= A.length; i<L; i++){
           tem= A[i].selectorText? [A[i].selectorText, 
A[i].style.cssText]: [A[i]+''];
            if(s.test(tem[0])) SA[SA.length]= tem;
        }
    }
    return SA.join('\n\n');
}
       console.log(getDefinedCss ('ui-helper-hidden'));

                  </script>

Let me know if it works for you.