How to check if two numbers are sequential in JS? Codewars Kata

I’m trying to solve this kata:

You are given a list of unique integers arr, and two integers a and b. Your task is to find out whether or not a and b appear consecutively in arr, and return a boolean value (True if a and b are consecutive, False otherwise).

It is guaranteed that a and b are both present in arr.

Test examples:

consecutive([1, 3, 5, 7], 3, 7), false
consecutive([1, 3, 5, 7], 3, 1), true 
consecutive([1, 6, 9, -3, 4, -78, 0], -3, 4), true

This is what I have so far:

for (let i = 0; i < arr.length; i++) {
  let index2 = arr.indexOf(b)
  let index1 = arr.indexOf(a)

    let diff = (index2) - (index1)

    if (diff > 1) {
        console.log(diff, 'false');
        return false
    } else {
        console.log(diff, 'true');
        return true
    }
}

The test examples are passing but then when I submit the solution, some other tests are not passing. I don’t get to see the tests that are not passing so I’m stuck on this. Also, I thought that, in case a and b are the same number, so in case I had

cons([4, 6, 4, 5, 6], 4, 4)

my solution wouldn’t pass this test, so how could I improve it?