Isomorphic Strings - Given two strings s and t, determine if they are isomorphic

Isomorphic Strings:

Given two strings s and t, determine if they are isomorphic.
All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character, but a character may map to itself.

Example 1:

Input: s = "egg", t = "add"
Output: true

Example 2:

Input: s = "foo", t = "bar"
Output: false

Example 3:

Input: s = "paper", t = "title"
Output: true

Constraints:

1 <= s.length <= 5 * 104
t.length == s.length
s and t consist of any valid ascii character.

Solution:

                                    /**
                                    * @param {string} s
                                    * @param {string} t
                                    * @return {boolean}
                                    */
                                   let size = 256;
                                   var isIsomorphic = function(str1, str2) {
                                              
                                           let m = str1.length;
                                           let n = str2.length;
                                             
                                           // Length of both strings must be same
                                           // for one to one corresponance
                                           if(m != n)
                                               return false;
                                                 
                                           // To mark visited characters in str2
                                           let marked = new Array(size);
                                             
                                           for(let i = 0; i < size; i++)
                                               marked[i]= false;
                                             
                                             
                                           // To store mapping of every character
                                           // from str1 to that of str2 and
                                           // Initialize all entries of map as -1.
                                           let map = new Array(size);
                                           map.fill(0);
                                             
                                           for(let i = 0; i < size; i++)
                                               map[i]= -1;
                                         
                                           // Process all characters one by on
                                           for (let i = 0; i < n; i++)
                                           {
                                                 
                                               // If current character of str1 is
                                               // seen first time in it.
                                               if (map[str1[i].charCodeAt()] == -1)
                                               {
                                                     
                                                   // If current character of str2
                                                   // is already seen, one to
                                                   // one mapping not possible
                                                   if (marked[str2[i].charCodeAt()] == true)
                                                       return false;
                                     
                                                   // Mark current character of
                                                   // str2 as visited
                                                   marked[str2[i].charCodeAt()] = true;
                                     
                                                   // Store mapping of current characters
                                                   map[str1[i].charCodeAt()] = str2[i].charCodeAt();
                                               }
                                     
                                               // If this is not first appearance of current
                                               // character in str1, then check if previous
                                               // appearance mapped to same character of str2
                                               else if (map[str1[i].charCodeAt()] != str2[i].charCodeAt())
                                                   return 0;
                                           }
                                     
                                           return 1;
                                   };
                          

Output:

Isomorphic Strings