Find the missing character and their index – JS

var arr = ['a', 'b', 'd', 'e', 'f', 'g'];

function findMissingLetterWithIndex(arr) {
  for (let i = 0; i < arr.length - 1; i++) {
    const currentCharCode = arr[i].charCodeAt(0);
    const nextCharCode = arr[i + 1].charCodeAt(0);
    
    if (nextCharCode - currentCharCode > 1) {
      return {
        missingLetter: String.fromCharCode(currentCharCode + 1),
        missingIndex: i + 1
      };
    }
  }
}

const result = findMissingLetterWithIndex(arr);
console.log("Missing letter:", result.missingLetter); // Output: Missing letter: c
console.log("Missing index:", result.missingIndex);   // Output: Missing index: 2

The missing letter is ‘c’, and its index is 2.