let input arr=[9,4,4,8,90,4,9,4,4,4,4,4,4,4,4,4,7,9,2,4,4,4,4,4,8,4,4,4,4];

let output arr=[1,7,9,11,13,15,19,21,25,27];

Above is an input array of numbers which contain mostly 4, if there is a pair of 4 which means (Input elements has 2 of the number 4 consecutively), its array position will be displayed in the output array. I have tried my code below but I am still unsure on how to solve this :). May I know how to solve this?

console.clear();
let arr=[8,4,4,4,4,4,4,4,4,4,7,9,2,4,4,4,4,4,8,4,4,4,4];

console.log("his")
for (let i=0;i<arr.length;i++){
if (arr[i]!==arr[i+1] &&arr[i]!==4 ){
console.log(i)
}
if (arr[i]!==arr[i+1] &&arr[i+1]!==4 ){
console.log(i+1)
}

}

>Solution :

You could look to the next item and if the last index is not in the result array, the add the actual index to the result.

const
    input = [9, 4, 4, 8, 90, 4, 9, 4, 4, 4, 4, 4, 4, 4, 4, 4, 7, 9, 2, 4, 4, 4, 4, 4, 8, 4, 4, 4, 4],
    result = input.reduce((r, v, i, a) => {
        if (v === a[i + 1] && r[r.length - 1] !== i - 1) r.push(i);
        return r;
    }, []);

console.log(...result);