Using indexOf() to compare characters in an Array

Question

  function mutation(arr) {

  var tester = arr[1].split('');

  for (var i = 0; i < tester.length; i ++) {
    if (!arr[0].indexOf(tester[i])) return false;
  }
  return true;
  }

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

Here I should 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.

I do not see any problems with this code but it passes like only 90% of the tests and I do not know why. And I can not see a pattern there — what exact conditions should I meet to fail the test.

Answer 1

The indexOf() method returns the index within the calling String object of the first occurrence of the specified value, starting the search at fromIndex. Returns -1 if the value is not found.

String.prototype.indexOf() returns -1 if value was't found, that is why your statement doesn't work.

Change to:

if (arr[0].indexOf(tester[i]) < 0) return false;