Custom flat function for arrays in javascript/node.js

CustomFlat.js

Array.prototype.customFlat = function(depth = 1) {
    let result = []
    for (let arr of this) {
        if (Array.isArray(arr) && depth > 0) {
            result.push(...arr.customFlat(depth-1))
        } else {
        result.push(arr)
        }
    }
    return result
}

let a = [
    [1,2],
    [3,4],
    [[5,6]],
    [[[7,8]]],
    [9,10]
]

console.log(a.customFlat(3))