js 字符串查找相同字母最长子串

var str ="sdfvadsvadsaaasdfvsdassssvweswwwWWWwwvdsvsssssddddfffff";
        var reg = /(\w)\1+/g;
        var a,max=[""];
        while((a = reg.exec(str)) != null){
            if(max[0].length < a[0].length){
                max[0] = a[0]
            }else if(max[0].length == a[0].length){
                max.push(a[0])
            } 
        }
        console.log(max)