Such anagram

anagram.js

function addLetters(s){    
   var letters = {};

   for(var i = 0; i < s.length; i++){
       var letter = s[i].toLowerCase();

       if(letter != " "){
           if(letters[letter]){
               letters[letter] += 1;
           } else {
               letters[letter] = 1;
           }
       }
   }

   return letters;
}

function isAnagram(s1, s2){

   var letters1 = addLetters(s1);
   var letters2 = addLetters(s2);

   for(var letter in letters1){    
       if(letters1[letter] != letters2[letter]){
          /*
            Здесь можно возвращать массив вроде [false, letter] чтобы определять, в какой букве разница,
            и даже [false, letter, letters2[letter] - letters1[letter]] чтобы определять разницу по количеству букв.
          */
           return false;
       }
   }
   
   for(var letter in letters2){
      if(letters1[letter] != letters2[letter]){
         return false;
      }
   }
   
   return true;
 
}

console.log(isAnagram("стационар", "соратница"));
console.log(isAnagram("покраснение", "пенсионерка"));
console.log(isAnagram("внимание", "Вениамин"));
console.log(isAnagram("апельсин", "спаниель"));
console.log(isAnagram("eleven plus two", "twelve plus one"));
console.log(isAnagram("statue of liberty", "built to stay free"));
console.log(isAnagram("older and wiser", "I learned words"));

// false
console.log(isAnagram("стационар", "сортница"));
console.log(isAnagram("покранение", "пенсионерка"));
console.log(isAnagram("внимание", "Вениамина"));
console.log(isAnagram("апельсина", "спаниель"));
console.log(isAnagram("eleven plus one", "twelve plus one"));
console.log(isAnagram("statue of paris", "built to stay free"));
console.log(isAnagram("older and wiser", "you learned words"));

круто!