Remove adjacent duplicates on array

Question

Suppose we have an array of numbers like the next one:

const input = [2, 2, 0, 2, 3, 3, 0, 0, 1, 1];

The goal is to remove duplicates values, but only if they are adjacent. So, the expected output for the previous sample should be:

[2, 0, 2, 3, 0, 1]

So far, I managed to almost solve this using a recursive approach, but for some reason that I can't figure, the generated result is not returned (however, you can see it on the log before the returning condition).

const input = [2, 2, 0, 2, 3, 3, 0, 0, 1, 1];

const remAdjDups = (arr, output = []) =>
{
    if (!arr.length)
    {
        console.log("Result before return: ", output);
        return output;
    }

    if (arr[0] === arr[1])
    {
        arr.splice(1, 1);
        remAdjDups(arr, output);
    }
    else
    {
        remAdjDups(arr.slice(1), output.concat(arr[0]));
    }
}

let out = remAdjDups(input.slice());
console.log("output: ", out);

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So, first and mainly, I will like to understand what is happening with my approach, and second I'm open to any other approach (of any type) that could solve this problem.

---

Updated Solution

Just in case anyone is interested, I have finally solve this problem using recursion this way. I know filter solution is shorted and elegant, but I was training solving by recursion.

const input = [2, 2, 0, 2, 3, 3, 0, 0, 1, 1, 1, 1, 1];

const remAdjDups = ([x, y, ...rest], out = []) =>
{
    if (!rest.length)
        return (x === y) ? [...out, x] : [...out, x, y];
    else if (x === y)
        return remAdjDups([x, ...rest], out);
    else
        return remAdjDups([y, ...rest], [...out, x]);
}

let out = remAdjDups(input.slice());
console.log("output: ", out);

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Answer 1

Regarding your solution, just add return before remAdjDups(arr...

P.S.

I used Array.prototype.filter for that

const input = [2, 2, 0, 2, 3, 3, 0, 0, 1, 1];

const result = input.filter((i,idx) => input[idx-1] !== i)

console.log(result)

Answer 2

You can use filter

const input = [2, 2, 0, 2, 3, 3, 0, 0, 1, 1];

const result = input.filter((i,index) => {
 if(index != 0){
  return input[index-1] !== i
 } 
 return i
})

console.log(result)