javascript basic algorithm(12)--Mutations

Description: 

                  Return true if the string in the first element of the array contains all of the letters of the string in the second element of the array. For example, ["hello", "Hello"], should return true because all of the letters in the second string are present in the first, ignoring case.

Review: indexOf(); 

Solution 1:

Thinking process:

      1. convert each element into lowercase.

      2. iterate                                                   // by using indexOf(elem[i]) to search  

Code:  

               funciton mutation(arr){

                var elem0 = arr[0].toLowerCase;

                var elem1 = arr[1].toLowerCase;

                for(var i=0; i < elem1.length; i++){

                var check = elem0.indexOf(elem1[i]);

                if (check === -1) {

                 return false;

}

               else{return true;}

}

}

mutation(["hello", "hey"]);