js检测css样式的兼容问题

<script>

            function supportCss3(style) { 
                var prefix = ['webkit', 'Moz', 'ms', 'o'], 
                    i, 
                    humpString = [], 
                    htmlStyle = document.documentElement.style, 
                    _toHumb = function (string) { 
                    return string.replace(/-(\w)/g, function ($0, $1) { 
                    return $1.toUpperCase(); 
                    }); 
                    }; 
 
            for (i in prefix) 
                humpString.push(_toHumb(prefix[i] + '-' + style)); 
 
                humpString.push(_toHumb(style)); 
 
            for (i in humpString) 
                if (humpString[i] in htmlStyle) 
                return true; 
 
                    return false; 
                
            }
               //测试用例
                alert(supportCss3('opacity'));
                if(supportCss3('opacity') == true){
                    
                    document.getElementById('header').style.backgroundColor = 'rgba(51,51,51,0.3)';
                    }
                    else{
                        
                        document.getElementById('header').style.backgroundColor = '#333';
                        }
</script>