Flattening an array recursively (withoout looping) javascript

I'm practicing recursion and am trying to flatten an array without looping (recursion only). As a first step I did the iterative approach and it worked, but am stuck on the pure recursion version:

function flattenRecursive(arr) {
    if (arr.length === 1) {
        return arr;
    }

    return Array.isArray(arr) ? arr = arr.concat(flattenRecursive(arr)) : flattenRecursive(arr.slice(1))
}

console.log(flattenRecursive([
    [2, 7],
    [8, 3],
    [1, 4], 7
])) //should return [2,7,8,3,1,4,7] but isn't - maximum call stack error


//working version (thanks @Dave!):

function flattenRecursive(arr) {
    if (arr.length === 1) {
        return arr;
    }

    return arr[0].concat(Array.isArray(arr) ? flattenRecursive(arr.slice(1)) : arr);
}

console.log(flattenRecursive([
    [2, 7],
    [8, 3],
    [1, 4], 7
]))

//returns [ 2, 7, 8, 3, 1, 4, 7 ]

via Chebli Mohamed