Flatten array using recursion

Question

I have to flatten an array using recursion, but I am not able to understand, why this code is always outputting an empty array. Can someone please help me here. This is the code

function flatten(arr){
    let result = [];
    function helper(arr) {
        
        for(let i = 0; i<arr.length; i++){
            if(Array.isArray(arr[i])){
                helper(arr[i]);
                return result;
            }else{
                result.push(arr[i]);
            }
        }
    }
    return result;
}