Normalize CSS Selectors

// Unfortunately there is no native way to 'normalize a selector'
// This little trick makes the browser to do the job instead of implementing your tokenizer and parser

function normalizeSelectors(aSelector) {

    var parser   = new DOMParser(),
        string   = '<style>' + aSelector + '{}</style>',
        doc      = parser.parseFromString(string, "text/html"),
        cssRules = doc.querySelector('style').sheet.cssRules;
    
        if (cssRules[0]) {
            return cssRules[0].selectorText
        } else {
            // selector is invalid...
            return null
        }
}

normalizeSelectors('foo     bar') //  -> returns 'foo bar'
normalizeSelectors('foo     bar: fee') //  -> returns null as this is a bad selector

demo at http://jsfiddle.net/4ez3k/1/