JavaScript Find the first non-consecutive number in Array

We have to write a function that takes in an array and returns the index of the first nonconsecutive number from it. Like all the numbers will be in an arithmetic progression of common difference 1. But the number, which violates this rule, we have to return its index.

If all the numbers are in perfect order, we should return -1.

Let’s write the code for this function −

Example

const arr = [1,2,3,4,5,6,8,9,10];
const secondArr = [3,4,5,6,7,8,9,10,11,12,13,14,15];
const findException = (arr) => {
   for(let i = 0; i < arr.length-1; i++){
      if(arr[i+1] - arr[i] !== 1){
         return i+1;
      };
   };
   return -1;
};
console.log(findException(arr));
console.log(findException(secondArr));

Output

The output in the console will be −

6
-1