(function(){

    var hashMap = {};
    
    function isAnagram (str1, str2) {
    
        if(str1.length !== str2.length){
            return false;
        }
        
        // Create hash map of str1 character and increase value one (+1).
        createStr1HashMap(str1);

        // Check str2 character are key in hash map and decrease value by one(-1);
        var valueExist = createStr2HashMap(str2);

        // Check all value of hashMap keys are zero, so it will be anagram.
        return isStringsAnagram(valueExist);
    }
    
    function createStr1HashMap (str1) {
        [].map.call(str1, function(value, index, array){
            hashMap[value] = value in hashMap ?  (hashMap[value] + 1) : 1;
            return value;
        });
    }
    
    function createStr2HashMap (str2) {
        var valueExist = [].every.call(str2, function(value, index, array){
            if(value in hashMap) {
                hashMap[value] = hashMap[value] - 1;
            }
            return value in hashMap;
        });
        return valueExist;
    }
    
    function isStringsAnagram (valueExist) {
        if(!valueExist) {
            return valueExist;
        } else {
            var isAnagram;
            for(var i in hashMap) {
                if(hashMap[i] !== 0) {
                    isAnagram = false;
                    break;
                } else {
                    isAnagram = true;
                }
            }
    
            return isAnagram;
        }
    }
    
    isAnagram('stackoverflow', 'flowerovstack'); // true
    isAnagram('stackoverflow', 'flowervvstack'); // false
    
})();